Method for operating a vehicle drive train with a drive motor, an output and a transmission which is arranged between the drive motor and the output

ABSTRACT

A method for operating a vehicle drivetrain (1) includes proceeding, in the presence of the demand for activation of the engine start-stop function of the vehicle drivetrain (1) and a simultaneously shut-down drive machine (2), from an operating state of the vehicle drivetrain (1) during which a sailing operating function of the vehicle drivetrain (1) is active, during which the drive machine (2) is decoupled from the drive output (3), during which the positively engaging shift element (F) is open and during which a rotational speed (n_ab) of the drive output (3) is higher than a defined rotational speed at which a rotational speed difference between shift element halves of the positively engaging shift element (F) lies within a rotational speed range within which the positively engaging shift element (F) is transferrable into the closed operating state, and actuating the positively engaging shift element (F) in a closing direction no later than when the defined rotational speed is reached.

FIELD OF THE INVENTION

The invention relates generally to a method for operating a vehicledrivetrain having a drive machine, a drive output and a gearbox which isarranged in the power flow between the drive machine and the driveoutput.

BACKGROUND

A multi-stage gearbox having nine forward gears and having one reversegear is known from DE 10 2008 000 429 A1. The multi-stage gearboxincludes four planetary sets, eight rotatable shafts and six shiftelements. The first and the second planetary set form a shiftableupstream gear set, whereas the third and the fourth planetary setsconstitute a so-called main gear set. The carrier plates or webs of thefirst and second planetary sets are coupled to one another by one of therotatable shafts, which is connected to an element of the main gear set.The ring gear of the first planetary set is coupled to the sun gear ofthe second planetary set with a further shaft of the rotatable shafts,which is detachably connectable to a drive shaft with a clutch.

The sun gear of the first planetary set is couplable via a further shaftof the rotatable shafts to a housing of the multi-stage gearbox througha brake and is connectable to the drive shaft with a clutch. The ringgear of the second planetary set is couplable via a shaft to the housingthrough a brake. In turn, a further shaft of the rotatable shafts isconnected at least to one element of the main gear set and is couplablethrough the brake to the housing. A further shaft of the rotatableshafts is connected to a further element of the main gear set and isconnectable to the drive shaft through a shift element in the form of aclutch, whereas a drive output shaft is connected to at least onefurther element of the main gear set. At least two of the shift elementsof the multi-stage gearbox are in the form of positively engaging shiftelements, which are deactivated only during upshifts.

To save fuel, vehicles are equipped with so-called engine start-stopfunctions. In vehicle ranges close to standstill, these functions andcertain actuation logic allow for a drive machine to be transferred intoa shut-down operating state. Here, through engine start-stop functions,it is sought for the power flow between the drive machine and the driveoutput of the vehicle to be produced within short operating times in theregion of a gearbox upon starting of the engine.

SUMMARY OF THE INVENTION

Example aspects of the present invention provide a method for operatinga vehicle drivetrain having a drive machine, a drive output and agearbox which is arranged in the power flow between the drive machineand the drive output and is configured with at least one positivelyengaging shift element and with a plurality of frictionally engagingshift elements through which method sailing operation of a vehicleequipped with the vehicle drivetrain can be deactivated with at leasthigh spontaneity.

In the method according to example aspects of the invention foroperating a vehicle drivetrain having a drive machine, a drive outputand a gearbox which is arranged in the power flow between the drivemachine and the drive output, wherein the gearbox is configured with atleast one positively engaging shift element and with a plurality offrictionally engaging shift elements, through which a plurality oftoothed gear pairings of a gear set of the gearbox can be engaged anddisengaged in order to realize different transmission ratios of thegearbox, only some of the transmission ratios being realizable using thepositively engaging shift element, it is provided that, in the presenceof a demand for activation of an engine start-stop function of thevehicle drivetrain, the drive machine is decoupled from the drive outputand is shut down, and the positively engaging shift element istransferred into or left in the closed operating state of the positivelyengaging shift element.

According to examples aspects of the invention, in the presence of ademand for activation of the engine start-stop function of the vehicledrivetrain, it is provided that, in the case of a simultaneouslyshut-down drive machine, proceeding from an operating state of thevehicle drivetrain during which a coasting operating function of thevehicle drivetrain is active, during which the shut-down drive machineis decoupled from the drive output and the positively engaging shiftelement is open, and during which a rotational speed of the drive outputis higher than a defined rotational speed at which a rotational speeddifference between shift element halves of the open positively engagingshift element lies within a rotational speed range within which thepositively engaging shift element can be transferred into a closedoperating state, the positively engaging shift element is actuated in aclosing direction at or before the time when the defined rotationalspeed is reached.

Using the above-described approach according to example aspects of theinvention, the sailing operating state of the vehicle drivetrain can bedeactivated in a simple manner with high spontaneity, and the enginestart-stop function of the vehicle drivetrain can be activated withinshort operating times, because the positively engaging shift element tobe activated which is present in the open operating state is, during acoasting process of a vehicle equipped with the vehicle drivetrainduring which the positively engaging shift element to be activated atleast intermittently attains an at least approximately synchronizedoperating state, transferable into the closed operating state as desiredwithout additional measures.

To avoid undesirably high loads in the region of the positively engagingshift element to be activated, the actuation of the positively engagingshift element in a closing direction is, in an easily implementablevariant of the method according to the invention, ended when the openoperating state of the positively engaging shift element is detectedwhen the vehicle is at a standstill.

In a further advantageous variant of the method according to theinvention, the sailing operating function can be deactivated withdesired high spontaneity if, in the presence of an active sailingoperating function, the present operating state of the vehicledrivetrain and the transmission ratio that has to be engaged in thegearbox during a restart of the shut-down drive machine as a result ofactivation of the engine start-stop function are identified, in eachcase at least those shift elements which have to be activated in orderto realize the transmission ratio that has to be engaged in the gearboxin the event of a departure from the sailing operating function beingheld in an operating state prepared for an activation.

In a further advantageous variant of the method according to theinvention, drag torques, which impair an efficiency of the vehicledrivetrain, in the region of the gearbox and of the drive machine areavoided if, in the presence of an active sailing operating function, thegear set of the gearbox is transferred, by actuation of a plurality offrictionally engaging shift elements, into an at least partially blockedoperating state in which the gearbox input shaft is held rotationallyfixed and the gearbox output shaft connected to the drive output isrotatable.

Using a further variant of the method according to the invention, anincrease in spontaneity upon departure from the sailing operating stateis achieved, in that, in the case of a power flow between the drivemachine and the drive output being interrupted in the region of thegearbox, all of those frictionally engaging shift elements which in aclosed operating state permit a rotation of the gearbox output shaft aretransferred into the closed operating state. Through such an approach,in the case of a correspondingly designed gearbox, which has for examplea structural design similar to the multi-stage gearbox described in theintroduction and known from the prior art, a multiplicity of the shiftelements is transferred into the closed operating state. Then, upondeparture from the sailing operating state, a demanded operating statecan be realized in the gearbox predominantly as desired within desiredshort operating times as there are fewer shift elements that have to betransferred from their open operating state into their closed operatingstate than there are shift elements that are already present in theclosed operating state and have to be deactivated or opened. This isadvantageous because closed frictionally engaging shift elements can betransferred into their open operating state more quickly than openfrictionally engaging shift elements can be transferred into theirclosed operating state.

If the sequence of the shift elements that have to be successivelyactuated for the partial blocking of the gear set is selected in eachcase in a manner dependent on the present operating state profile of thevehicle drivetrain, the sailing operating state can be activated withhigh spontaneity in the event of a corresponding demand, and the vehicledrivetrain can be transferred within short operating times, and thuswith high spontaneity, into the operating state that has to be producedas a result of the demand for the deactivation of the sailing operatingstate.

The gearbox can be operated with further improved spontaneity during adeparture from the sailing operating state if, in the presence of anactive sailing operating state of the vehicle drivetrain, actuationforces of the frictionally engaging shift elements are in each caselowered to a level at which the frictionally engaging shift elements arein each case still in a slippage-free operating state and proceedingfrom which the shift elements can be entirely activated or deactivatedwithin short operating times. In the case of a departure from thesailing operating state, the shift elements that are charged withreduced pressure can be deactivated or evacuated within short operatingtimes proceeding from the lower actuation pressure level, and can thusbe opened more quickly. At the same time, the shift elements that haveto be activated to the full extent in order to realize the operatingstate that has to be produced after the deactivation of the sailingoperating state can be transferred from the reduced pressure level intothe fully activated operating state more quickly than fully open shiftelements.

Actuation forces of the shift elements that have to be held in ortransferred into the closed operating state in order to realize theafter the departure from the sailing operating function of the vehicledrivetrain and as a result of the activation of the engine start-stopfunction, are raised to the level corresponding thereto while thefurther frictionally engaging shift elements are opened. Thus, in turn,the demanded operating state of the gearbox can be realized to thedemanded or desired extent within short operating times.

In a further advantageous variant of the method according to theinvention, in order to generate a rotational speed difference requiredfor the closure of the positively engaging shift element between shiftelement halves of the positively engaging shift element which is presentin the open operating state, the torque transfer capacity of at leastone of the shift elements that are actuated for the at least partialblocking of the gear set is varied. With this measure, it is for examplepossible for so-called tooth-on-tooth positions in the region of thepositively engaging shift element to be activated to be easilyeliminated with little outlay in the presence of a rotational speed ofthe drive machine greater than zero.

In a further advantageous variant of the method according to theinvention, in the presence of a demand for activation of the enginestart-stop function and an associated demand for realizing, in thegearbox, a transmission ratio which can be engaged in the gearbox byactivation of the positively engaging shift element and in the event ofidentification of the open operating state of the positively engagingshift element, it is provided that a synchronization transmission ratiois engaged in the gearbox first for the realization of which thepositively engaging shift element is present in the open operatingstate. To implement a subsequent transmission ratio change proceedingfrom the synchronization transmission ratio in the direction of thedemanded transmission ratio, a frictionally engaging shift element hasto be deactivated and the positively engaging shift element has to beclosed. Thus, the positively engaging shift element is in each casecapable of being transferred, proceeding from defined operating statesof the gearbox, from an open operating state into a closed operatingstate within short operating times and with little outlay in terms ofopen-loop and closed-loop control.

If the demand for activation of the sailing operating function is, inthe presence of a simultaneously activated engine start-stop function,triggered in the event of an exceedance of a defined threshold value ofthe rotational speed of the drive output, an undesirably large increasein transmission-internal drag torques is limited in a simple manner.

Alternatively or in addition to this, in advantageous variants of themethod according to the invention, the demand for activation of thesailing operating function is, in the presence of a simultaneouslyactivated engine start-stop function, triggered in the event of anexceedance of the defined threshold value of the rotational speed of thedrive output for longer than a predefined time period or after a drivingdistance longer than a defined driving distance has been traveled,whereby excessively high rotational speeds in the gearbox, and forexample dry running of bearing units of the gearbox, are permanentlyavoided with little outlay.

The positively engaging shift element is transferred into an at leastapproximately load-free operating state through at least a partialengagement, in the gearbox, of that transmission ratio for therealization of which the positively engaging shift element has to betransferred into the open operating state and at least the torquetransfer capacity of one of the frictionally engaging shift elements hasto be varied, and said positively engaging shift element is opened whenthe at least approximately load-free operating state is attained, inorder that, in the presence of high gearbox drag torques, proceedingfrom an operating state of the vehicle drivetrain in which the enginestart-stop function is active and the positively engaging shift elementis closed, the sailing operating state is activated with desired highspontaneity and the positively engaging shift element is transferredinto its open operating state within short operating times.

If the torque transfer capacity of that frictionally engaging shiftelement which has to be actuated in order to engage the transmissionratio which relieves the positively engaging shift element of load is,when the sailing operating function is active, raised from a value ofzero to a level which relieves the positively engaging shift element ofload, the positively engaging shift element can be transferred into anat least approximately load-free operating state with little open-loopand closed-loop control outlay without causing any discontinuities inthe profile of a torque acting in the region of the drive output of thevehicle drivetrain.

In a further variant of the method according to the invention, when theopen operating state of the positively engaging shift element isidentified, the frictionally engaging shift element is transferred intoits open operating state, and in this way, the power flow between thedrive machine and the drive output is interrupted in the region of thegearbox in a simple manner, and the sailing operation of the vehicledrivetrain is activated with high spontaneity.

In the presence of a demand for realizing a sailing operating state ofthe vehicle drivetrain during which the drive machine is active and thepower flow between the drive output is interrupted in the region of thegearbox, it is provided in a further variant of the method according tothe invention that the active drive machine is disconnected from thedrive output by opening of one of the shift elements that are held in aclosed operating state in order to realize the operating state presentbefore the demand for decoupling of the active drive machine. Followingthis, the shift elements are actuated, in a manner dependent on thepresent operating state profile of the vehicle drivetrain and withactive drive machine decoupled, such that the shift elements that haveto be activated in order to realize the transmission ratio to be engagedin the gearbox in the presence of a demand for coupling of the activedrive machine to the drive output are, at the time of the demand,partially already in the activated operating state, and the active drivemachine is connected to the drive output by closure of a further shiftelement of the further shift elements, and the transmission ratiodemanded in a manner dependent on the present operating state of thevehicle drivetrain is engaged in the gearbox.

A sailing operating state, which reduces the fuel consumption of avehicle, can be realized with little outlay, and an operating state,demanded as a result of a demand for deactivation of or departure fromthe sailing operating state, of the vehicle drivetrain, in particular inthe region of the gearbox, can be implemented or achieved with highspontaneity because, while the sailing operating state is active, it isthe case according to the invention that so-called gearspeed tracking isperformed in a manner dependent on the operating state profile of thevehicle drivetrain, through which, upon a departure from the sailingoperating state, the transmission ratio that has to be realized in eachcase in a manner dependent on the presently prevailing operating stateof the vehicle drivetrain can be engaged in the gearbox within shortoperating times.

In this variant, the drive machine is in the active operating statebefore the activation of the sailing operating state, while the sailingoperating state is active and after the deactivation of the sailingoperating state. In this way, the gearbox can, in a manner which isexpedient with regard to structural space and costs, be supplied withhydraulic fluid over the entire operating range of the vehicledrivetrain using a gearbox main pump which is driven by the gearboxinput shaft, without the need to provide an electrically operatedauxiliary pump for this purpose, which requires additional structuralspace and increases production costs of the gearbox.

In an advantageous variant of the method according to the invention, inthe presence of a demand for realizing the sailing operating stateproceeding from an operating state of the gearbox for the realization ofwhich the positively engaging shift element is closed, the closedpositively engaging shift element is transferred into an open operatingstate. Through this approach, it is achieved that, in the presence of adecoupled drive machine, drag torques in the gearbox resulting from theclosed operating state of the positively engaging shift element thatadversely affect the gain in efficiency resulting from activation of thesailing operating state and the rotational speeds which place anundesired burden on the components of the gearbox and which are lower inthe open operating state of the positively engaging shift element are tobe avoided.

To be able to implement a demand for deactivation of the sailingoperating state with the greatest possible spontaneity, in the presenceof a demand for realizing the sailing operating state proceeding from anoperating state of the gearbox for the realization of which the furtherpositively engaging shift element is open, a further positively engagingshift element is transferred into its closed operating state if anoperating state profile of the vehicle drivetrain is identified duringwhich a subsequent demand for coupling-on of the active drive machine orfor deactivation of the sailing operating state triggers, in thegearbox, an engagement of a transmission ratio for the realization ofwhich the further positively engaging shift element has to be activated.Thus, it is possible in a simple manner to avoid a situation in which,in the event of a departure from sailing triggered by a load demand froma driver, a downshift in the gearbox is demanded, during which aclaw-type shift element has to be activated. This is made possible withlittle outlay by transferring the further positively engaging shiftelement into its closed operating state already during the sailingoperating state of the vehicle drivetrain.

If the further positively engaging shift element is closed when therotational speed of the drive output is lower than a threshold value,the actuation of the further positively engaging shift element is basedon a speed-dependent strategy, which can be implemented with littleoutlay, for claw conditioning. For example, upon transition into sailingproceeding from an operating state of the vehicle drivetrain in which ahigh gear with a low transmission ratio is engaged in the gearbox in thelower speed range of the vehicle, the open positively engaging shiftelement is advantageously transferred into its closed operating state,because a downshift in the direction of a lower gear with highertransmission ratio is triggered in the gearbox in any case upon adeactivation of the sailing operating state. By contrast to this, thelatter approach may be disturbing and disadvantageous in higher speedranges of a vehicle, because the further positively engaging shiftelement then does not, upon a departure from sailing or upon adeactivation of the sailing operating state, have to be held in theclosed operating state in order to realize the then demanded operatingstate of the gearbox or of the vehicle drivetrain.

In general, through the speed-dependent selection of whether the furtherpositively engaging shift element is activated or left in the openoperating state upon a transition into the sailing operating state, ahigh level of dynamics is achieved both during a transition into sailingand during a departure from sailing. This is because, while the sailingoperating state is active, the further positively engaging shift elementis transferred into its closed operating state only if it is detectedthat the further positively engaging shift element has to be transferredinto its closed operating state upon a deactivation of the sailingoperating state in order to realize the demanded operating state of thevehicle drivetrain.

If, during the activation process of the further shift element, a clutchwhich is arranged in the power flow of the vehicle drivetrain betweenthe drive machine and the gearbox is opened and the rotational speed ofa gearbox input shaft is adjusted in the direction of zero by actuationof at least one of the frictionally engaging shift elements in order togenerate, between shift element halves of the further positivelyengaging shift element which is in the open operating state, arotational speed difference within a defined rotational speed differencerange such as is required for the closure of the further positivelyengaging shift element, stalling of the drive machine is prevented withlittle outlay if, for the synchronization of the further positivelyengaging shift element, the rotational speed of the gearbox input of thegearbox has to be adjusted substantially in the direction of zero. Thus,the stalling can be prevented, if the rotational speed of the gearboxinput is adjusted substantially in the direction of zero.

This approach is particularly advantageous if the clutch is a converterlock-up clutch which is assigned to a hydrodynamic torque converter.

To generate an at least approximately load-free operating state of thefurther positively engaging shift element, such as is required for theclosure of the further positively engaging shift element, it is providedin a further advantageous variant of the method according to theinvention that the torque transfer capacity of at least one frictionallyengaging shift element is varied. With this measure, it is for examplethe case that so-called tooth-on-tooth positions in the region of thefurther positively engaging shift element to be activated can be easilyeliminated with little outlay in the presence of a rotational speed ofthe drive machine greater than zero.

In addition to the variation of the torque transfer capacity of thefrictionally engaging shift element, it is also possible for therotational speed of the drive machine to be varied in order to eliminatea tooth-on-tooth position in the region of the further positivelyengaging shift element to be activated. In addition or alternatively tothis, it may in turn also be provided that the torque transfer capacityof the clutch between the drive machine and the gearbox is varied inorder to impart a disturbance torque to the gearbox and eliminate theblocking in the region of the further positively engaging shift elementto be activated.

Furthermore, it may also be provided that, during the activation processof the further positively engaging shift element to be activated,positive locking between the shift element halves that have to be placedin engagement with one another has already been set in the region of thefurther positively engaging shift element, but the further positivelyengaging shift element has not yet reached its fully closed operatingstate, and the closing process cannot be performed as desired despite acorresponding actuation in a closing direction. In this case, it is inturn the case that the torques that impede the completion of theactivation process of the further positively engaging shift element andwhich act on the further positively engaging shift element can bereduced by variation of the torque transfer capacity of at least onefrictionally engaging shift element, and the complete sliding-inmovement in the region of the further positively engaging shift elementcan be implemented as desired. Such torques which impede the closingprocess of a positively engaging shift element result for example fromdrag torques or other influences, which can be reduced as desired usingthe above-described approaches in order to be able to operate a vehicledrivetrain with high dynamics and ensure availability in the case ofjamming claw-type shift elements.

The vehicle drivetrain and the gearbox can be operated with highspontaneity if, in the presence of a demand for realizing a neutraloperating state of the gearbox, for which the power flow has to beinterrupted in the region of the gearbox through corresponding actuationof the shift elements and for which the further positively engagingshift element has to be opened, the gearbox, in sailing operation of thevehicle drivetrain, is prepared for the engagement of a transmissionratio by virtue of the further positively engaging shift element beingheld in its closed operating state and an actuation logic of the shiftelements being selected allowing a neutral operating state of thegearbox to be realized in which the further positively engaging shiftelement is present in its closed operating state.

Aside from the improvement of the actuation spontaneity, it is achievedwith the latter variant of the method according to the invention that ademanded neutral operating state of the gearbox is implemented withalready-known actuation sequences, whereby there is no need fordevelopment and implementation of further actuation routines whichrequire additional hardware resources. Furthermore, with this variant ofthe method according to the invention, a gearspeed disengagementsequence which can be performed within short operating times isrealized, during which gearspeed disengagement sequence the power flowis initially fully depleted before the further positively engaging shiftelement is disengaged in order to realize the neutral gearspeed demandedas a result of the demand for the neutral operating state of thegearbox.

The sailing operating state can be easily deactivated with highspontaneity if, when the sailing operating state is active and theactive drive machine is decoupled, and in the presence of an operatingstate of the vehicle drivetrain in which the further positively engagingshift element is closed and proceeding from which, in the event of ademand for the coupling of the drive machine to the gearbox, atransmission ratio has to be engaged for the realization of which boththe further positively engaging shift element and the positivelyengaging shift element have to be closed, the positively engaging shiftelement is closed when an at least approximately synchronized operatingstate is attained.

In a variant of the method according to the invention that can beimplemented with little outlay in terms of open-loop and closed-loopcontrol, it is provided that, during an operating state profile of thevehicle drivetrain during which the rotational speed of the drive outputand/or the rotational speed of the gearbox input approaches a rotationalspeed which corresponds to the synchronous rotational speed which isset, in the event of a demand for deactivation of the sailing operatingstate and a resulting demand for coupling of the active drive machine tothe gearbox, by closure of the positively engaging shift element in thecase of a simultaneously closed further positively engaging shiftelement, the positively engaging shift element is closed when arotational speed difference between the shift element halves of thepositively engaging shift element which is present in the open operatingstate lies within a defined rotational speed difference window.

In a further advantageous variant of the method according to theinvention, during an operating state profile of the vehicle drivetrainduring which the active drive machine is operated at the level of theidle rotational speed and the synchronous rotational speed of thegearbox input, which is set in the case of a transmission ratio engagedin the gearbox through the closed further positively engaging shiftelement and through additional closure of the positively engaging shiftelement, is higher than the idle rotational speed of the drive machine,the rotational speed of the gearbox input is, through a positive enginetorque intervention, raised from the idle rotational speed in thedirection of the synchronous rotational speed, whereby the vehicledrivetrain can be operated with high spontaneity in the event of acorresponding demand.

In an advantageous variant of the method according to the invention, tobe able to determine the synchronization point of the open positivelyengaging shift element to the required extent within short operatingtimes, the torque transfer capacity of a shift element between the drivemachine and the gearbox is, during the determination of thesynchronization point of the open positively engaging shift element,adjusted to a defined level at which the rotational speed of the drivemachine and the rotational speed of the gearbox input at leastapproximately correspond to one another.

In a further advantageous variant, the shift element between the drivemachine and the gearbox is, during the closure of the positivelyengaging shift element, at least partially opened in order, with littleoutlay, to avoid stress being placed on the drive machine during adverseoperating state profiles of the vehicle drivetrain.

In a further variant of the method according to the invention, forhighly spontaneous operation of the vehicle drivetrain, it is providedthat, during operating state profiles of the vehicle drivetrain duringwhich events which vary the rotational speed of the drive output, suchas actuation of a service brake of the vehicle, occur and change thesynchronization process of the positively engaging shift element to beactivated and trigger a demand for coupling of the active drive machine,a transmission ratio is engaged in the gearbox first, for therealization of which the positively engaging shift element is opened.Following this, in the gearbox, a transmission ratio is engaged for therealization of which a closed frictionally engaging shift element has tobe deactivated and the positively engaging shift element has to beclosed.

Thus, it is achieved in a simple manner that, during operating stateprofiles during which the adjustment of the positively engaging shiftelement to a synchronized state during the gearspeed tracking isinfluenced by external effects such as a braking action, a load demandor other measures which vary the drive output rotational speed, thegearspeed tracking is not imperatively performed or is terminated backin the direction of the current gear, and the non-positive engagementbetween the drive machine and the gearbox is established. The operatingstate of the vehicle drivetrain, and in particular of the gearbox, thatis demanded here is initially implemented by engagement of a so-calledsupporting or synchronizing gearspeed in the gearbox and a subsequentdownshift under power while the positively engaging shift element isengaged.

If, during operating state profiles of the vehicle drivetrain duringwhich events which vary the rotational speed of the drive output occurand vary the synchronization process of the positively engaging shiftelement to be engaged, it is provided that, in the gearbox, inpreparatory fashion, such transmission ratios are engaged in each casethat the synchronization point of the positively engaging shift elementto be activated can be attained on the basis of the presently prevailingrotational speeds of the drive output, of the gearbox input and of thedrive machine and the present gradients of the profiles of saidrotational speeds, and the positively engaging shift element istransferred into its closed operating state in an at least approximatelysynchronized operating state, the positively engaging shift element canbe transferred into its closed operating state with high spontaneitywithin short operating times without further measures. Using thissituation-based adaptation of the respectively prepared synchronizationgearspeed in the gearbox, it is the case in particular during afreewheeling process of a vehicle that multiple rotational speed windowscan be selected within which the positively engaging shift element to beactivated has its respective synchronization point.

If the vehicle drivetrain is configured, in the region between the drivemachine and the gearbox, with a hydrodynamic torque converter and aconverter lock-up clutch assigned to the torque converter, the converterlock-up clutch has to be actuated, and the torque transfer capacitythereof possibly varied, in a manner dependent on the respectivelypresent operating state of the vehicle drivetrain and also in a mannerdependent on the respectively demanded operating state of the vehicledrivetrain in order to be able to perform changes in operating state ofthe vehicle drivetrain with high spontaneity without impairing drivingcomfort in the process.

For example, it is particularly advantageous if, before an activationprocess of the positively engaging shift element or of the furtherpositively engaging shift element, the torque transfer capacity of theconverter lock-up clutch is set to a level at which only little slippageoccurs in the region of the converter lock-up clutch or the converterclutch is operated without slippage, in order to minimizediscontinuities in the profile of a rotational speed difference betweenshift element halves of the positively engaging shift elements. Ifrotational irregularities in the region of the drive machine falsify therotational speed signal of the positively engaging shift elements, thetorque transfer capacity of the converter lock-up clutch is reduced tosuch an extent that the rotational speed of the drive machine and therotational speed of the gearbox input substantially correspond to oneanother, but rotational speed oscillations of the drive machine are notfully imparted to the gearbox input, and are introduced merely indampened fashion into the gearbox during slippage operation of theconverter lock-up clutch.

This approach is based on the realization that rotational speedoscillations and varying rotational speed differences between therotational speed of the drive machine and the rotational speed of thegearbox input give rise to undesired oscillations in the profile of therotational speed difference of the positively engaging shift elements,which prevent comfortable and load-free engagement of a positivelyengaging shift element.

During the closing process of the positively engaging shift element orof the further positively engaging shift element, it is possible, owingto adverse operating state profiles of the vehicle drivetrain, for asituation to arise in which a torque which impairs the engagement orclosing process of the positively engaging shift elements prevails atthe positively engaging shift elements in each case when the converterlock-up clutch is in a closed operating state or close to its closedoperating state.

To be able to perform the closing process as desired within shortoperating times with simultaneously high driving comfort, it is possiblefor the torque transfer capacity of the converter lock-up clutch to beadjusted during the activation process of one of the positively engagingshift element such that the converter lock-up clutch is operated inslipping fashion and the torque that acts in each case at the positivelyengaging shift element to be closed prevails at the positively engagingshift element with a magnitude which promotes the closure of thepositively engaging shift element. This approach makes it possible in asimple manner for the torque which, after the activation of the clawclutch, acts on the positively engaging shift element to be closed to beat least partially reduced by virtue of the converter lock-up clutchbeing opened. By contrast to this, closure of the converter lock-upclutch rather causes the torque that prevails in the region of thepositively engaging shift element or of the further positively engagingshift element to be increased, whereas an opening of the converterlock-up clutch reduces the respectively prevailing torque. Withcorresponding actuation of the converter lock-up clutch, the likelihoodof so-called claw jamming is thus reduced. In this way, greateravailability of the gearbox when a sailing operating state is active isensured.

If, as a result of a demand for the deactivation of the sailingoperating state of the vehicle drivetrain, an operating state of thevehicle drivetrain is demanded in which the positively engaging shiftelement is closed, it is provided that, in a first phase of theadjustment of the positively engaging shift element to be closed to atarget rotational speed, the converter lock-up clutch is held in itsclosed operating state. It is thus ensured that the rotational speed ofthe gearbox input substantially corresponds to the rotational speed ofthe drive machine. Shortly before the synchronous rotational speed ofthe positively engaging shift element to be closed is reached, it isnecessary for the converter lock-up clutch to be transferred into itsopen operating state in order for the torque prevailing at thepositively engaging shift element to be closed to be reduced as desiredas a function of the rotational speed difference in the region of ahydrodynamic torque converter, and/or for the torque that prevails atthe positively engaging shift element be closed during the engagementprocess to be dampened to an extent that promotes the activation processof the positively engaging shift element, whereby, in turn, less clawjamming occurs, and an availability of the gearbox during the sailingoperating state is increased.

In an advantageous variant of the method according to the invention, inthe presence of a demand for activation of a sailing operating functionof the vehicle drivetrain in the presence of a simultaneously activatedengine start-stop function, the positively engaging shift element isopened, while the drive machine is left in both its decoupled andshut-down operating state. Using this approach, a closed positivelyengaging shift element is transferred into its open operating state whenthe sailing operating function is active, whereby only low losses andloads arise in the gearbox during sailing operation.

If the sequence of the shift elements that have to be actuated insuccession for the partial blocking of the gear set is selected in eachcase in a manner dependent on the present operating state profile of thevehicle drivetrain, it is possible, in the event of a correspondingdemand, for the sailing operating state to be deactivated with highspontaneity and for the vehicle drivetrain to be transferred withinshort operating times, and thus with high spontaneity, into theoperating state that has to be produced as a result of the demand fordeactivation of the sailing operating state.

In a further variant of the method according to the invention, a demandfor activation of the engine start-stop function proceeding from anoperating state of the vehicle drivetrain during which the gearbox ispresently being transferred, on the basis of a previous demand foractivation of the sailing operating function, in the direction of anoperating state demanded for the realization of the sailing operatingfunction is implemented with high spontaneity by virtue of the fact thatthe closed positively engaging shift element is left in its closedoperating state, and shift elements actuated as a result of the demandfor activation of the sailing operating function are actuated to anextent required for realizing the operating state of the gearbox thathas to be realized as a result of the demand for activation of theengine start-stop function.

By contrast to this, in a further advantageous variant, a demand foractivation of the engine start-stop function proceeding from anoperating state of the vehicle drivetrain during which the gearbox ispresently being transferred, on the basis of a previous demand foractivation of the sailing operating function, towards realizing ordisplaying an operating state demanded by the sailing operatingfunction, the already open positively engaging shift element istransferred into its closed operating state, and shift elements actuatedas a result of the demand for activation of the sailing operatingfunction are actuated to an extent required for realizing the operatingstate of the gearbox that has to be realized as a result of the demandfor activation of the engine start-stop function, in order to implementthe demand with high spontaneity.

In the presence of a demand for activation of the sailing operatingfunction proceeding from an operating state of the gearbox for therealization of which the positively engaging shift element is closed,the closed positively engaging shift element is, in an advantageousvariant of the method according to the invention, transferred into anopen operating state, whereby undesirably high drag losses in the regionof the gearbox are avoided in a simple manner.

In an advantageous variant of the method according to the invention,drag torques and component loads arising in the region of the gearbox,which in turn arise inter alia from rotational speed differences in theregion of bearing points of the gearbox, are reduced as desired byvirtue of the gearbox being transferred into the operating state inwhich the power flow between the drive machine and the drive output isinterrupted by opening of a frictionally engaging shift element and agearbox output shaft operatively connected to the drive output isrotatable.

In the presence of a demand for realizing a sailing operating state ofthe vehicle drivetrain, during which the drive machine is shut down andthe power flow between the drive machine and the drive output isinterrupted in the region of the gearbox, proceeding from an operatingstate of the vehicle drivetrain in which the drive machine is active andis connected via the gearbox to the drive output and a rotational speedof a gearbox output is higher than a threshold and in the presence of anoperating state of the gearbox in which the further positively engagingshift element is open, the power flow between the drive machine and thedrive output is, in a further advantageous variant of the methodaccording to the invention, disconnected in the region of the gearbox byvirtue of at least one frictionally engaging shift element being opened.It is furthermore provided that the further positively engaging shiftelement is closed at or before the timein the presence of a demand fordeparture from the sailing operating state and for realizing a demandedoperating state of the vehicle drivetrain in which the drive machine isactive and the power flow between the drive machine and the drive outputis produced by virtue of a transmission ratio being engaged in theregion of the gearbox, for the realization of which transmission ratiothe further positively engaging shift element has to be transferred intothe closed operating state.

Using this variant of the approach according to the invention, a sailingoperating state, which reduces a fuel consumption of a vehicle, can berealized with little outlay, and an operating state, demanded as aresult of a demand for deactivation of or departure from the sailingoperating state, of the vehicle drivetrain, in particular in the regionof the gearbox, can be implemented or achieved with high spontaneity,because, while the sailing operating state is active, it is the casethat so-called gearspeed tracking is performed in a manner dependent onthe operating state profile of the vehicle drivetrain, through which,upon a departure from the sailing operating state, the transmissionratio that has to be realized in each case in a manner dependent on thepresently prevailing operating state of the vehicle drivetrain isengaged in the gearbox within short operating times. Here, in thepresence of a demand for departure from the sailing operating state, itis additionally checked whether an operating state of the vehicledrivetrain is demanded, for the realization of which the furtherpositively engaging shift element has to be transferred into or held ina closed operating state. In the case of a positive result of the check,the further positively engaging shift element, which is present in theopen operating state, is closed at or before the timein the presence ofsuch a demand, in order to increase the actuation spontaneity of thegearbox and thus of a vehicle equipped therewith.

If, in the presence of a demand for realizing a sailing operating state,the further positively engaging shift element is closed before the drivemachine is shut down, it is possible in a simple manner to realize ahydraulic supply to the gearbox using a gearbox main pump driven by thedrive machine, and for an electrically driveable auxiliary pump that maybe provided to be designed with a relatively low power capacity. In thisway, it is in turn possible to reduce production costs of the gearboxand a structural space requirement and also a load on an onboardelectrical system. Furthermore, upon a departure from the sailingoperating state in the direction of an operating state of the vehicledrivetrain or of the gearbox for which the further positively engagingshift element has to be transferred into the closed operating state, thefurther positively engaging shift element is already present in theclosed operating state, whereby the gearbox can be operated with highspontaneity and a demanded operating state of the vehicle drivetrain canbe realized within short operating times.

As an alternative to this, it may also be provided that, in the presenceof a demand for realizing a sailing operating state, the furtherpositively engaging shift element is closed after the shut-down of thedrive machine, wherein then, upon transition into the sailing operatingstate, the vehicle drivetrain can likewise be operated with highspontaneity, because the so-called engine-stop enable signal can betriggered immediately upon transition into the sailing operating state.Furthermore, the vehicle drivetrain and the gearbox can also, upon adeparture from the sailing operating state, be operated with highspontaneity if, upon the departure from the sailing operating state, thevehicle drivetrain and the gearbox are to be transferred into anoperating state in which the further positively engaging shift elementhas to be transferred into or held in an open operating state.

In an advantageous variant of the method according to the invention, thegear set of the gearbox is held in the at least partially blockedoperating state at least until a rotational speed of the drive machineis lower than a threshold value. Thus, with little outlay, a fast enginerundown is realized and a resonance rotational speed range, whichimpairs driving comfort, is run through within short operating timesduring the engine rundown. Furthermore, an undesired increase of therotational speed of the gearbox input or of the gearbox input shaft as aresult of an excessively early elimination of the blocking operatingstate of the gear set of the gearbox during the shutdown of the drivemachine, which under some circumstances gives rise to a load reversal inthe vehicle drivetrain as a result of crossing of the profiles of therotational speed of the drive machine and of the gearbox input, isavoided.

If a converter lock-up clutch provided between the gearbox and the drivemachine for the purposes of locking up a hydrodynamic torque converteris transferred into a closed operating state in the presence of anactive sailing operating state and when the drive machine is in ashut-down state, a synchronous rotational speed of the gearbox inputrotational speed, which synchronous rotational speed corresponds to theoperating state of the vehicle drivetrain that is to be realized, can beset in a defined manner through possible rotational speed adjustment ofthe rotational speed of the drive machine. Furthermore, so-calledconverter slippage that occurs in the region of a hydrodynamic torqueconverter when the converter lock-up clutch is open does not have to betaken into consideration in the presetting of the target rotationalspeed of the drive machine, whereby actuation outlay of the vehicledrivetrain is low.

The vehicle drivetrain and the gearbox can be operated with highspontaneity if, in the presence of a demand for deactivation of thesailing operating state, the further positively engaging shift elementis transferred into or left in its open operating state, and if theoperating state of the gearbox that has to be realized in a mannerdependent on a present operating state profile of the vehicle drivetrainin the case of a deactivated sailing operating state can be producedonly when the further positively engaging shift element is in an openstate.

An increase in spontaneity upon departure from the sailing operatingstate is achieved, using a further variant of the method according tothe invention, in that, in the case of a power flow between the drivemachine and the drive output being interrupted in the region of thegearbox, all of those frictionally engaging shift elements which in aclosed operating state permit a rotation of the gearbox output shaft aretransferred into the closed operating state. Using such an approach, inthe case of a correspondingly designed gearbox, which has for example astructural design similar to the multi-stage gearbox described in theintroduction and known from the prior art, a multiplicity of the shiftelements is transferred into the closed operating state. Then, upondeparture from the sailing operating state, a demanded operating statecan be realized in the gearbox predominantly as desired within desiredshort operating times as there are fewer shift elements that have to betransferred from their open operating state into their closed operatingstate than there are shift elements that are already present in theclosed operating state and have to be deactivated or opened. This isadvantageous because closed frictionally engaging shift elements can betransferred into their open operating state more quickly than openfrictionally engaging shift elements can be transferred into theirclosed operating state.

In a further variant of the method according to the invention that canbe implemented with little outlay in terms of actuation, an interruptionof the power flow between the drive machine and the drive output in theregion of the gearbox is detected if a deviation between the rotationalspeed of the gearbox input shaft and the product of the rotational speedof the gearbox output shaft and the transmission ratio engaged in thegearbox at the present operating point of the vehicle drivetrain isgreater than a threshold value.

In a further advantageous variant of the method according to theinvention, the present operating state of the vehicle drivetrain and thetransmission ratio that has to be engaged in the gearbox upon adeparture from the sailing operating state are determined while thesailing operating state is active, provided that in each case at leastthose shift elements which have to be activated in order to realize thetransmission ratio to be engaged in the gearbox upon a departure fromthe sailing operating state are held in an operating state prepared foran activation of the shift elements. Using this approach, whichcharacterizes a so-called gearspeed tracking routine when the sailingoperating state is active, it is achieved with little outlay that agearbox can, upon a departure from the sailing operating state, betransferred within short operating times into the operating statethereby demanded, and can thus be operated with high spontaneity.

In an advantageous variant of the method according to the invention,discontinuities in the profile of a drive output rotational speed areavoided in that that frictionally engaging shift element which has to beopened for the separation of the power flow between the drive machineand the drive output in the region of the gearbox is, in the presence ofa demand for departure from the sailing operating state, activated onlywhen a blocking state of the gear set of the gearbox has beeneliminated.

To further improve the actuation spontaneity of the gearbox, it may beprovided that, in the presence of a demand for deactivation of thesailing operating state, it is checked whether a transmission ratio thathas to be engaged in the gearbox while the sailing operating state isactive in a manner dependent on the present operating state of thevehicle drivetrain corresponds to a transmission ratio that has to beengaged in the gearbox in a manner dependent on the event that demandsthe deactivation of the sailing operating state. In the event of adeviation being determined, the transmission ratio demanded by the eventis engaged in the gearbox. Thus, with little outlay, a situation isprevented in which, immediately after the departure from the sailingoperating state, the operating state demanded and produced by thedeactivation of the sailing operating state is immediately departed fromagain during the course of a further transmission ratio change, and theultimately demanded operating state is produced in the gearboximmediately upon the departure from the sailing operating state.

In a further advantageous variant of the method according to theinvention, a restart of the drive machine is performed upon departurefrom the sailing operating state taking into consideration agearbox-side rotational speed setpoint. The power flow between the drivemachine and the drive output is produced in the region of the gearboxonly when the rotational speed of the drive machine exceeds thesynchronous rotational speed of the gearbox input shaft, whichsynchronous rotational speed corresponds to the rotational speed of thegearbox output shaft. Synchronous rotational speed is set when thedemanded transmission ratio is engaged in the gearbox. Thus, anundesired crossing of rotational speeds between the rotational speed ofthe drive machine and the rotational speed of the gearbox output shaft,and an associated load reversal in the vehicle drivetrain, which impairsdriving comfort to an undesired extent, are avoided.

Both the features specified in the patent claims and the featuresspecified in the following exemplary embodiments of the subject matteraccording to the invention are suitable for refining the subject matterof the invention in each case individually or in any desired combinationwith one another.

Further advantages and advantageous embodiments of the subject matteraccording to the invention emerge from the patent claims and from thefollowing exemplary embodiments described in principle below withreference to the drawing, wherein, for the sake of clarity, the samereference designations have been used for structurally and functionallyidentical components.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is more specifically illustrated as anexample on the basis of the attached figures. The following is shown:

FIG. 1 is a schematic illustration of a vehicle drivetrain having anautomatic gearbox in the form of a 9-speed gearbox;

FIG. 2 shows a shift table of the automatic gearbox as per FIG. 1;

FIG. 3 shows several profiles, versus the time t, of different operatingvariables of a vehicle drivetrain, which has the automatic gearbox asper FIG. 1, which, in accordance with a demand, is transferred into asailing operating state which is in turn deactivated at a later timepoint;

FIG. 4 is an illustration, corresponding to FIG. 3, of the profiles ofthe operating variables during an operating state profile whichsubstantially corresponds to an operating state profile based on theprofiles as per FIG. 3, wherein a shut-down process of a drive machineof the vehicle drivetrain is started already at a time point from whichthe demand for activation of the sailing operating state is present;

FIG. 5 shows the profiles of the operating variables in the presence ofan active sailing operating state and a departure from the sailingoperating state in the direction of an operating state of the vehicledrivetrain in which a positively engaging shift element has to betransferred into or held in a closed operating state;

FIG. 6 shows the profiles of the operating variables of the vehicledrivetrain in the presence of an active sailing operating state which isdeactivated only shortly before the vehicle comes to a standstill;

FIG. 7 shows multiple profiles, versus the time t, of differentoperating variables of the vehicle drivetrain as per FIG. 1 which, inaccordance with a demand, is transferred into a sailing operating statewhich is in turn deactivated at a later time point;

FIG. 8 shows the profiles of the operating variables of the vehicledrivetrain in the presence of an active sailing operating state which isdeactivated only shortly before the vehicle comes to a standstill,wherein a synchronization point of a positively engaging shift elementto be activated is attained in the case of a constant rotational speedof a drive machine of the vehicle drivetrain in conjunction with specialgearspeed tracking;

FIG. 9 shows the profiles of the operating variables of the vehicledrivetrain in the case of an active sailing operating state which isdeactivated before the vehicle comes to a standstill, wherein asynchronization point of a positively engaging shift element to beactivated is enabled through a targeted engine torque intervention;

FIG. 10 shows the profiles of the operating variables of the vehicledrivetrain in the presence of an active sailing operating state, whichis deactivated as a result of intense deceleration of a vehicle equippedwith the vehicle drivetrain;

FIG. 11 shows the profiles of the operating variables of the vehicledrivetrain in the presence of an active sailing operating state, whichis deactivated on the basis of a power demand from a driver;

FIG. 12 shows multiple profiles, versus the time t, of several operatingvariables of the vehicle drivetrain as per FIG. 1 which set with thetime t during the implementation of a variant of the method according tothe invention;

FIG. 13 shows multiple profiles, of several operating variables of thevehicle drivetrain as per FIG. 1 which set with the time t during theimplementation of a further variant of the method according to theinvention;

FIG. 14 shows multiple profiles, versus the time t, of several operatingvariables of the vehicle drivetrain as per FIG. 1 which set with thetime t during the implementation of a variant of the method according tothe invention;

FIG. 15 shows multiple profiles of several operating variables of thevehicle drivetrain as per FIG. 1 which set with the time t during theimplementation of a further variant of the method according to theinvention;

FIG. 16 shows multiple profiles, versus the time t, of several operatingvariables of the vehicle drivetrain as per FIG. 1 which set with thetime t during the implementation of a variant of the method according tothe invention; and

FIG. 17 shows multiple profiles of several operating variables of thevehicle drivetrain as per FIG. 1 which set with time t during theimplementation of a further variant of the method according to theinvention.

DETAILED DESCRIPTION

Reference will now be made to embodiments of the invention, one or moreexamples of which are shown in the drawings. Each embodiment is providedby way of explanation of the invention, and not as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be combined with another embodiment to yield stillanother embodiment. It is intended that the present invention includethese and other modifications and variations to the embodimentsdescribed herein.

FIG. 1 is a highly schematic illustration of a vehicle drivetrain 1having a drive machine 2, a drive output 3 and a gearbox 4 arranged inthe power flow between the drive machine 2 and the drive output 3. Thegearbox 4 includes six shift elements A to F, wherein the shift elementsB, C, D and E are in the present case in the form of frictionallyengaging shift elements, whereas the shift elements A and F arepositively engaging shift elements. Here, the shift elements C, D and Fconstitute so-called brakes, whereas the shift elements B, E and A arein the form of clutches. In general, using the shift elements A to F,multiple toothed gear pairings of a gear set 5 of the gearbox 4 can beactivated and deactivated in order to realize, as listed in FIG. 2,different transmission ratios “1” to “9” for forward travel and onetransmission ratio “R” for reverse travel, wherein only some of thetransmission ratios “1” to “7” for forward travel can be realized usingthe positively engaging shift element A in conjunction with the furthershift elements B to E.

FIG. 2 shows a shift table of the gearbox 4, wherein, in the shifttable, in each case those shift elements A to F which are denoted by acircle have to be held in or transferred into a closed operating statein order to realize one of the transmission ratios “1” to “R”, whereasthe respective further shift elements A to F have to be transferred intoor held in their open operating state. Furthermore, the penultimatecolumn of the shift table specifies in each case the transmission ratiovalue corresponding to the transmission ratio “1” to “R” engaged in thegearbox 4, while the ratio step present between in each case twomutually adjacent transmission ratios is specified in the final columnof the shift table. Here, the first transmission ratio “1” for forwardtravel has the transmission ratio value 4.70, whereas the secondtransmission ratio “2” for forward travel that can be engaged in thegearbox 4 has a transmission ratio value of 2.84. Between the firsttransmission ratio “1” for forward travel and the second transmissionratio “2” for forward travel, the gearbox has a ratio step of 1.65.Altogether, the gearbox 4 has, owing to the configuration, an overallspread of 9.81.

Furthermore, those shift elements A to F which, in the presence of anactive sailing operating state of the vehicle drivetrain 1, have to beheld in the closed operating state in a manner dependent on therespectively present operating state of the vehicle drivetrain 1 aredenoted by a square, whereas a so-called sailing clutch, which is heldin the open operating state during the sailing operating state and whichis transferred into its closed operating state upon a departure from thesailing operating state in order to couple the drive machine 2 to thedrive output 3 as demanded in the region of the gearbox 4, is denoted bya square arranged within a circle. Here, the shift logic characterizedby the squares and by the squares arranged within the circlesconstitutes a so-called standard logic in the active sailing operatingstate of the vehicle drivetrain 1. For example, in the presence of anactive sailing operating state using the standard shift logic, during anoperating state of the vehicle drivetrain 1 in which the secondtransmission ratio “2” for forward travel has to be engaged in thegearbox 4 upon a departure from the sailing operating state, thefrictionally engaging shift element C is the sailing clutch, whereas thepositively engaging shift elements A and F are present in the closedoperating state.

As an alternative to this, in the presence of an active sailingoperating state, the gearbox 4 may also be actuated in accordance with afirst variant of the shift logic, wherein the shift elements A to Fwhich then have to be held in the closed operating state in each caseare denoted by a triangle, whereas the sailing clutch is in each casethe shift element F or E, which is denoted in each case by a trianglearranged within a circle.

Furthermore, it is also possible, in the presence of an active sailingoperating state, for the gearbox 4 to be actuated in accordance with asecond variant of the shift logic, wherein the shift elements that haveto be held in the closed operating state are denoted in each case by ahexagon, and the shift element E, D, C, B which constitutes the sailingclutch in each case is denoted by a hexagon arranged within a circle.

That transmission ratio range of the gearbox 4 which includes thetransmission ratios “1” to “9” for forward travel may basically bedivided functionally into three transmission ratio sub-ranges. Here, afirst transmission ratio sub-range includes the transmission ratios “1”to “4”, for the realization of which in each case both the positivelyengaging shift element A and the positively engaging shift element Fhave to be held in or transferred into the closed operating state, andin each case one of the frictionally engaging shift elements D, C, B orE additionally have to be closed. The adjoining second transmissionratio sub-range includes the transmission ratios “5” to “7”, for therealization of which in each case only the positively engaging shiftelement A, in addition to two further frictionally engaging shiftelements B and E, or C and E, or D and E, respectively, have to be heldin the closed operating state. The third transmission ratio sub-rangewhich in turn adjoins the second transmission ratio sub-range includesthe transmission ratios “8” and “9” for forward travel, which areengaged by simultaneous closure of the three frictionally engaging shiftelements C, D and E, or D, B and E, in the gearbox 4.

In the event of changes in transmission ratio in the gearbox 4 within atransmission ratio sub-range, in each case only one frictionallyengaging shift element D, C, B or E, or B, C, D or C, B, respectively,has to be deactivated, and one other frictionally engaging shift elementE, B, C, D, or D, C, B, or B, C, respectively, has to be activated. Bycontrast to this, in the event of a transmission ratio change in thegearbox 4 in the case of which a transmission ratio of one of thetransmission ratio sub-ranges has to be disengaged and a transmissionratio of a further transmission ratio sub-range has to be engaged in thegearbox 4, it is necessary in each case to perform an activation ordeactivation of at least one of the positively engaging shift elements Aand F, which is realized using conventional shift routines during normaldriving operation of the vehicle drivetrain 1.

However, if the vehicle drivetrain 1 is in its sailing operating stateand if, as described in more detail further below, the gearbox 4 isactuated, in a manner dependent on the respectively presently prevailingoperating state of the vehicle drivetrain, such that, upon a departurefrom sailing, the demanded operating state of the vehicle drivetrain 1can be realized within short operating times and thus with highspontaneity by activation of only one of the shift elements A to F, theapproaches described in more detail below have to be performed in amanner dependent on the operating state.

At the gearbox input side, the gearbox 4 is operatively connected by ahydrodynamic torque converter 7 to the drive machine 2. In the presentcase, the hydrodynamic torque converter 7 is assigned a so-calledconverter lock-up clutch 8, the torque transfer capacity of which isvaried, in a manner known per se, in a manner dependent on the operatingstate in order to minimize losses in the region of the hydrodynamictorque converter 7. At the gearbox output side, the gearbox 4 isoperatively connected by a gearbox output shaft 9 to the drive output 3.

In the present case, the gearbox 4 includes four planetary gear sets P1to P4, wherein the first and the second planetary gear set P1 and P2,which are preferably in the form of minus planetary gear sets, form ashiftable upstream gear set, whereas the third planetary gear set andthe fourth planetary gear set P3 and P4 form a so-called main gear set.A sun gear S3 of the third planetary gear set P3 is in the present casein fixed rotational connection with a sun gear S4 of the fourthplanetary gear set P4. When the positively engaging shift element F isin a closed operating state, the two sun gears S3 and S4 are in fixedrotational connection with a component 10 that is fixed with respect toa housing, and said sun gears rotate freely when the positively engagingshift element F is in an open operating state. The sun gear S3 mesheswith planet gears PR3 which are arranged rotatably on a planetarycarrier ST3 of the third planetary gear set P3. Furthermore, the planetgears PR3 are in engagement with a ring gear HR3 of the third planetarygear set P3. The sun gear S4 of the fourth planetary gear set P4 in turnmeshes with planet gears PR4, wherein the planet gears PR4 are arrangedrotatably on a planetary carrier ST4 and the planetary carrier ST4 is infixed rotational connection with the gearbox output shaft 9.Furthermore, the planet gears PR4 are in engagement with a ring gear HR4of the fourth planetary gear set P4, which in turn is in fixedrotational connection with the planetary carrier ST3 of the thirdplanetary gear set P3.

The planetary carrier ST3 of the third planetary gear set P3 can beplaced in operative connection with the gearbox input shaft 6 throughthe shift element E. The ring gear HR3 of the third planetary gear setP3 is in fixed rotational connection with a planetary carrier ST2 of thesecond planetary gear set P2, which in turn is operatively in fixedrotational connection with a planetary carrier ST1 of the firstplanetary gear set P1. Planet gears PR2 mounted rotatably on theplanetary carrier ST2 mesh both with a ring gear HR2 and with a sun gearS2 of the second planetary gear set P2, wherein the ring gear HR2 may bein fixed rotational connection with the component 10 that is fixed withrespect to a housing through the frictionally engaging shift element D.The sun gear S2 of the second planetary gear set P2 is in turn in fixedrotational connection with a ring gear HR1 of the first planetary gearset P1, which meshes with planet gears PR1, which in turn are inengagement with a sun gear S1 of the first planetary gear set P1. Thesun gear S1 may be in fixed rotational connection with the component 10that is fixed with respect to the housing through the frictionallyengaging shift element C and can be placed in operative connection withthe gearbox input shaft 6 through the frictionally engaging shiftelement B. Furthermore, when the shift element B is in a closedoperating state, the sun gear S1 may be in fixed rotational connectionwith the ring gear HR1 of the first planetary gear set P1 through thepositively engaging shift element A.

To be able to operate the vehicle drivetrain 1 with the least possiblefuel consumption of the drive machine 2 with simultaneously highspontaneity, the vehicle drivetrain 1 is, in a manner dependent on theoperating state, operated in the manner described in more detail belowon the basis of the illustrations as per FIG. 3 to FIG. 17.

FIG. 3 to FIG. 6 show multiple profiles, versus the time t, of differentoperating variables of the vehicle drivetrain 1, wherein the vehicledrivetrain 1 is, at a time point T0 indicated in more detail in FIG. 3,in an operating state in which the eighth transmission ratio “8” or theninth transmission ratio “9” for forward travel is engaged in thegearbox 4 and a rotational speed n_mot of the drive machine 2 is higherthan an idle rotational speed n_motLL of the drive machine 2. At thetime point T0, a demand is triggered for realizing a sailing operatingstate of the vehicle drivetrain 1 during which the drive machine 2 isshut down and the power flow between the drive machine 2 and the driveoutput 3 is interrupted in the region of the gearbox 4. Here, the demandfor the activation of the sailing operating state is triggeredproceeding from an operating state of the vehicle drivetrain 1 in whichthe drive machine 2 is active and is connected by the gearbox 4 to thedrive output 3. Furthermore, a rotational speed n_ab of the drive output3 is higher than a threshold value, which is greater than zero. With theeighth or ninth transmission ratio “8” or “9” for forward travelengaged, the positively engaging shift element A is open.

For the activation of the sailing operating state, proceeding from thetime point T1, the frictionally engaging shift element E is, bycorresponding lowering of an actuation pressure p_E in the mannerillustrated in FIG. 3, transferred into its open operating state over aperiod until a time point T2, and thus the power flow between the drivemachine 2 and the drive output 3 is disconnected in the region of thegearbox 4.

Furthermore, proceeding from the time point T0, the rotational speedn_mot of the drive machine 2 is progressively adjusted to theillustrated extent in the direction of the idle rotational speedn_motLL. The lowering of the torque transfer capacity of thefrictionally engaging shift element E has the effect that, proceedingfrom a time point T3 which lies between the time points T1 and T2, therotational speed n_t of the gearbox input shaft 6, hereinafter alsoreferred to as turbine rotational speed, deviates from the product ofthe rotational speed n_ab of the drive output 3 and the transmissionratio i_zielgang_sas presently engaged in the gearbox at the time pointT0. If the deviation between the turbine rotational speed n_t and thetransmission ratio i_zielgang_sas exceeds a threshold value kfl, then inthe present case, the disconnected power flow between the drive machine2 and the drive output 3 in the region of the gearbox 4 is detected. Inthe present case, this is the situation at a time point T4 which liesbetween the time points T3 and T2.

At the time point T4, with the ninth transmission ratio “9” for forwardtravel engaged in the gearbox 4, an actuation pressure p_C of thefrictionally engaging shift element C is raised in abrupt fashion, inthe manner illustrated in idealized form in FIG. 3, to the level of afast-charging pressure, and is maintained at said level until a timepoint T5. Subsequently, the actuation pressure p_C is lowered at thetime point T5 to an intermediate pressure level, and is raised in rampedfashion through two successive pressure ramps over a period until a timepoint T6, at which the frictionally engaging shift element C is in aslippage-free operating state. At the time point T6, the actuationpressure P_C is raised to a level at which the frictionally engagingshift element C is fully closed.

If, at the time point T0, the eighth transmission ratio “8” for forwardtravel is engaged in the gearbox 4, it is the case that, between thetime points T4 and T6, instead of the actuation pressure p_C, anactuation pressure p_B of the frictionally engaging shift element B isadjusted in the last-described manner in order to transfer thefrictionally engaging shift element B into the closed operating state inaddition to the frictionally engaging shift elements C and D.

In the closed operating state of the frictionally engaging shiftelements C, D and B, the gear set 5 of the gearbox 4 is in a partiallyblocked operating state in which the gearbox input shaft 6 is heldrotationally fixed and the gearbox output shaft 9 connected to the driveoutput 3 is rotatable. In the present case, in this operating state ofthe gearbox 4, an increase of an actuation pressure p_A of thepositively engaging shift element A occurs, whereby the positivelyengaging shift element A is transferred into its closed operating state.At the same time, the drive machine 2 is shut down, whereby therotational speed n_mot of the drive machine 2 falls in the direction ofzero. The demand that corresponds to this emerges from a profile MSFwhich, at the time point T6, jumps from the value 0 to 1 and thusactivates the engine-stop enable signal. Thus, at the time point T6, thesailing operating state demanded at the time point T0 is activated asdesired.

In the present case, the sailing operating state is demanded by a demandfrom a driver, for example by a release of an accelerator pedal and anactuation, preferably by the driver, of the service brake. In additionor as an alternative to this, it is also possible for the sailingoperating state to be demanded by a superordinate driving strategy if nodemand for power is made by the driver and it is additionally determinedthat a driving route, determined for example through the use of anavigation system, can be traveled at least in sections in sailingoperation with low fuel consumption.

In the present case, in the manner shown in FIG. 3, the vehicledrivetrain 1 remains in the sailing operating state up until a timepoint T7. At the time point T7, it is for example the case that thedriver actuates the accelerator pedal again and demands a correspondinglevel of power from the drive machine 2. This demand for power from thedriver has the effect that the profile MSF drops from the value one tothe value zero, and the engine-stop enable signal is deactivated. Thisin turn has the effect that the drive machine 2 is activated, and therotational speed n_mot of the drive machine 2 increases proceeding fromthe time point T7. To prevent an uncontrolled increase of the enginerotational speed n_mot, a gearbox-side engine target rotational speedsetpoint is triggered, which is implemented in accordance with theprofile n_motEGS. As a result of the activation of the engine targetrotational speed setpoint, the engine rotational speed n_mot is, at thetime point T7, raised to a level which lies above the rotational speedof the gearbox input shaft 6, which emerges from the product of thedrive output rotational speed n_ab and the transmission ratioi_zielgang_sas to be engaged in the gearbox 4 at the time point T7.

At the time point T7, since the vehicle drivetrain 1 is in a deactivatedsailing operating state, the transmission ratio engaged in the gearbox 4at the time point T0 has been established as desired. At time point T7,the ninth transmission ratio “9” or the eighth transmission ratio “8”for forward travel has to be engaged in the gearbox 4, the actuationpressure p_A of the positively engaging shift element A is lowered, andthe positively engaging shift element A is transferred into its openoperating state. At the same time, the actuation pressure p_C or theactuation pressure p_B of the frictionally engaging shift element C or Brespectively is lowered to zero in order to eliminate the blocking stateof the gear set 5 that was held between the time points T4 and T6.

With increasing rotational speed n_mot of the drive machine 2 and anelimination of the blocking state of the gear set 5, the turbinerotational speed n_t increases proceeding from a time point T8 whichfollows the time point T7, and said turbine rotational speed n_t followsthe profile of the rotational speed n_mot of the drive machine 2.Proceeding from a time point T9 which follows the time point T8, theactuation pressure p_E of the frictionally engaging shift element E is,in the manner shown in FIG. 3, prepared for the closing thereof during afast-charging phase, which lasts until a time point T10, and a followingcharging compensation phase, which lasts until a time point T11. Fromthe time point T9 onwards, the drive machine 2 is in the closed-looprotational speed control mode.

At the time point T11, the frictionally engaging shift element E is inan operating state in which the torque transfer capacity of thefrictionally engaging shift element E is substantially equal to zero anda further increase of the actuation pressure p_E results in an immediateincrease of the torque transfer capacity of the frictionally engagingshift element E. Proceeding from the time point T11, the actuationpressure p_E is increased by a pressure ramp which lasts until a timepoint T12. The actuation pressure p_E of the frictionally engaging shiftelement E is in the present case increased, at the time point T11, bythe first pressure ramp which follows the charging compensation phaseif, for the traction operation of the vehicle drivetrain 1 underconsideration here, the profile of the rotational speed n_mot of thedrive machine 2 has reached or even exceeded the profilen_ab*i_zielgang_sas, and a rotational speed difference Nd_Syn betweenthe shift element halves of the shift element E to be activated is closeto the synchronous rotational speed or less than or equal to a thresholdvalue.

By contrast to this, proceeding from the time point T11, the actuationpressure p_E of the shift element E to be activated is, in coastingoperation of the vehicle drivetrain 1 in a manner not illustrated in anymore detail, increased by the first pressure ramp which follows thecharging compensation phase if the profile of the rotational speed n_motof the drive machine 2 lies below or corresponds to the profilen_ab*i_zielgang_sas, and a rotational speed difference Nd_Syn betweenthe shift element halves of the shift element E to be activated is closeto the synchronous rotational speed or less than or equal to a thresholdvalue.

Following this, the actuation pressure p_E of the frictionally engagingshift element E is increased further by a further pressure ramp, thegradient of which is smaller than that of the pressure ramp presentbetween the time points T11 and T12. At the end of the further pressureramp, in the present case at the time point T13, the frictionallyengaging shift element E is present in a slippage-free operating state,and the turbine rotational speed n_t corresponds to the product of thedrive output rotational speed n_ab and the transmission ratioi_zielgang_sas demanded at the time point T7 and to be engaged in thegearbox 4, which transmission ratio in the present case correspondseither to the ninth transmission ratio “9” or the eighth transmissionratio “8”.

The engine rotational speed n_mot is adjusted to a level above theprofile n_ab*i_zielgang_sas through the gearbox-side engine targetrotational speed setpoint in order to avoid an undesired crossing ofrotational speeds between the rotational speed n_mot of the drivemachine 2 and the turbine rotational speed n_t during the establishmentof the power flow between the drive machine 2 and the drive output 3 inthe region of the gearbox 4, the turbine rotational speed n_t beingdetermined from the transmission ratio i_zielgang_sas to be engaged inthe gearbox 4 and the drive output rotational speed n_ab. A crossing ofrotational speeds between the engine rotational speed n_mot and theprofile n_ab*i_zielgang_sas gives rise to an undesired load reversal inthe vehicle drivetrain 1, which impairs driving comfort to an undesiredextent.

At the time point T14, the actuation pressure p_E of the frictionallyengaging shift element E is at the closing pressure level, and theoperating state of the vehicle drivetrain 1 demanded at the time pointT7 has been established as desired at the time point T14. After the timepoint T14, proceeding from which the sailing operating state of thevehicle drivetrain 1 has been ended, any demanded subsequent shifts canbe performed as desired in the gearbox 4.

The operating state profile of the vehicle drivetrain 1 forming thebasis of the profiles illustrated in FIG. 4 differs from the operatingstate profile of the vehicle drivetrain 1 forming the basis of theprofiles of the various operating variables of the vehicle drivetrain 1shown in FIG. 3 in that, during the operating state profile as per FIG.4, the rotational speed n_mot of the drive machine 2 is lowered in thedirection of zero already at the time point T5, that is to say in thepresent case at the end of the fast-charging phase of the shift elementC or B, respectively. By contrast to this, during the operating stateprofile as per FIG. 3, the engine rotational speed n_mot of the drivemachine 2 is lowered in the direction of zero only at the time point T6,at which the actuation pressure p_C or p_B, respectively, is raised tothe closing pressure level.

The approach as per FIG. 3 offers the possibility of enabling ahydraulic supply to the gearbox 4 using a gearbox main pump (notillustrated in any more detail in the drawing) which is driven by thedrive machine 2 via the gearbox input shaft 6, and the possibility foran electrically operated auxiliary pump of the gearbox 4 to be designedwith a lower power capacity. By contrast to this, during the operatingstate profile of the vehicle drivetrain 1 in FIG. 4, proceeding from thetime point T5, the hydraulic supply to the gearbox 4 must no longer beperformed entirely by the gearbox main pump but must be performedincreasingly by the electrical auxiliary pump of the gearbox 4, forwhich reason said auxiliary pump must be dimensioned correspondingly inorder to implement the approach as per FIG. 4.

Furthermore, during the operating state profile of the vehicledrivetrain 1 based on FIG. 4, the positively engaging shift element A isnot transferred into its closed operating state at the time point T6.Since, owing to the demand for deactivation of the coasting operatingstate present at the time point T7, an operating state of the vehicledrivetrain 1, it is necessary in the gearbox 4 to engage the eighthtransmission ratio “8” or the ninth transmission ratio “9” for forwardtravel, for the realization of which the positively engaging shiftelement A has to be transferred into or held in the open operatingstate, the positively engaging shift element A is left in its openoperating state at the time point T7 and, by contrast to the operatingstate profile of the vehicle drivetrain 1 as per FIG. 3, said positivelyengaging shift element does not have to be transferred into its openoperating state for the first time at the time point T7.

Thus, the approach described with regard to FIG. 4 has an advantage inrelation to the approach discussed with regard to FIG. 3. This advantageis that, in the gearbox 4 at the time point T6, it is not necessary forany present tooth-on-tooth positions in the region of the positivelyengaging shift element A. This advantage occurs because (1) the torquetransfer capacity of one of the three simultaneously closed shiftelements C, D or B is varied, removing the gear set 5 from its partiallyblocked operating state and (2) a rotational speed difference expedientfor the engagement of shift element A is established between shiftelement halves of the positively engaging shift element A. Furthermore,any present bracing states in the region of the positively engagingshift element A at the time point T7, at which the positively engagingshift element A is transferred into its open operating state during theoperating state profile according to FIG. 3, do not have to beeliminated by corresponding actuation of the torque transfer capacity ofthe shift element C or B which then additionally has to be deactivated,before the positively engaging shift element A can be transferred intoits open operating state in order to realize the ninth transmissionratio “9” or the eighth transmission ratio “8” for forward travel.

Furthermore, the actuation of the frictionally engaging shift element E,which has to be transferred into its closed operating state in order toestablish the power flow between the drive machine 2 and the driveoutput 3, can, from as early as the time point T7, at which the demandfor deactivation of the sailing operating state of the vehicledrivetrain 1 is triggered, be transferred into its closed state withgreater spontaneity than is possible during the operating state profileof the vehicle drivetrain 1 based on FIG. 3.

By contrast to this, the approach described with regard to FIG. 3,specifically the transfer of the positively engaging shift element Ainto its closed operating state as early as at the time point T6, hasadvantages in relation to the approach discussed with regard to FIG. 4with regard to the spontaneity of the vehicle drivetrain 1 if a demandfor deactivation of the sailing operating state of the vehicledrivetrain 1 demands an operating state of the vehicle drivetrain 1 forwhich, in the region of the gearbox 4, it is necessary to engage one ofthe transmission ratios “7” to “1” for forward travel, for therealization of which the positively engaging shift element A has to betransferred into or held in its closed operating state, because saidshift element is then already present in its closed operating state atthe time point T7.

FIG. 5 shows the profiles of the operating variables of the vehicledrivetrain 1 as per FIG. 3 and FIG. 4 during an operating state profileof the vehicle drivetrain 1 after the time point T6, at which thevehicle drivetrain 1 is already in the sailing operating state. Up to atime point T15, a superordinate driving strategy identifies that, in theevent of a possible departure from the sailing operating state of thevehicle drivetrain 1, the eighth transmission ratio “8” or the ninthtransmission ratio “9” for forward travel has to be engaged in thegearbox 4. At the time point T15, the driving strategy determines, inthe case of an active sailing operating state of the vehicle drivetrain1, that, in the event of a departure from the sailing operating state,the seventh transmission ratio “7” for forward travel has to be engagedin the gearbox 4. The positively engaging shift element A has alreadybeen transferred into its closed operating state at the time point T6,in the manner described with regard to FIG. 3.

Owing to the fact that the driving strategy has identified that theseventh transmission ratio “7” for forward travel has to be engaged inthe gearbox 4 proceeding from the time point T15, either the actuationpressure p_B of the frictionally engaging shift element B or theactuation pressure p_C of the frictionally engaging shift element C islowered at the time point T15 in order to increase the spontaneity ofthe gearbox 4, whereas the actuation pressure p_D of the frictionallyengaging shift element D is maintained at the closing pressure level ofthe shift element D. The actuation pressure p_B or the actuationpressure p_C of the frictionally engaging shift element B or C is inthis case higher, by an offset value, than a pressure value pf_min+Hysplus an offset value dependent on a hysteresis, which represents anactuation threshold above which the frictionally engaging shift elementsB, C and D are in a slippage-free operating state in the presence of anactive sailing operating state.

The pressure value pf_min+Hys plus a corresponding offset valuecorresponds to a pressure level above a transmission pressure level ofthe frictionally engaging shift elements B, C and D. It is therebyensured that, in the presence of the active sailing operating state, thefrictionally engaging shift elements B, C and D continue to be presentin the closed operating state as a result of the charging with such apressure level of the respective actuation pressure p_B, p_C or p_D, butwith a significantly lower torque transfer capacity. This offers theadvantage that, in the event of a failure, the risk of overdeterminacyof the gear set 5 of the gearbox 4 is reduced because, in the presenceof a corresponding torque, the shift elements B, C, D are transferred bythe latter into a slipping operation as desired, and thus a brakingtorque prevailing in the region of the gearbox output shaft 9 can belimited in a simple manner.

The spontaneity of the vehicle drivetrain 1 is increased, in particularin the region of the gearbox 4, by virtue of the fact that, in thepresence of a corresponding demand for deactivation of the sailingoperating state of the vehicle drivetrain 1 after the time point T15,only the frictionally engaging shift element E has to be closed, and thevehicle drivetrain 1 can be made available, within short operating timest, with the operating state demanded by the demand for deactivation ofthe sailing operating state.

In the present case, the vehicle drivetrain 1 remains in the sailingoperating state even after the time point T15. At a subsequent timepoint T16, the driving strategy identifies that the profilen_ab*i_zielgang_sas has reached a value at which a potential demand fordeactivation of the sailing operating state in turn demands an operatingstate of the vehicle drivetrain 1 for the establishment of which thesixth transmission ratio “6” or the fifth transmission ratio “5” has tobe engaged in the region of the gearbox 4. For this reason, at the timepoint T16, the actuation pressure p_C or the actuation pressure p_B ofthe frictionally engaging shift element C or of the frictionallyengaging shift element B, respectively, is increased as illustrated fromthe pressure level above the threshold value pf_min+Hys plus an offsetvalue which allows for a hysteresis in the direction of the closingpressure level in the manner presented in FIG. 5, whereas the actuationpressure p_D of the frictionally engaging shift element D, at the timepoint T17 at which the actuation pressure p_C or p_B, respectively,reaches the closing pressure level, lowered to a pressure level abovethe threshold value pf_min+Hys plus offset.

In the present case, at a time point T18, a demand for deactivation ofthe sailing operating state of the vehicle drivetrain 1 is triggered,wherein the departure from the sailing operating state of the vehicledrivetrain 1 is performed towards an operating state of the vehicledrivetrain 1 for which either the sixth transmission ratio “6” or thefifth transmission ratio “5” for forward travel has to be engaged in thegearbox 4. At the time point T18, the shift elements A to D are alreadyprepared for realizing such a demanded operating state of the vehicledrivetrain 1 and in particular of the gearbox 4. Therefore, proceedingfrom the time point T18, it is merely necessary for the frictionallyengaging shift element E to be transferred as demanded into its closedoperating state in the manner presented in FIG. 5.

The profile of the actuation pressure p_E of the frictionally engagingshift element E, the profile n_motEGS of the EGS engine targetrotational speed setpoint and the profile of the rotational speed n_motof the drive machine 2 substantially correspond, from the time point T18onwards, to those sections of said profiles which are shown in FIG. 3from the time point T9 onwards. Therefore, with regard to the actuationof the shift element E and the actuation of the drive machine 2proceeding from the time point T18, reference is made here, for the sakeof clarity, to the above description relating to FIG. 3 and to theapproach discussed there regarding the actuation of the shift element Eand of the drive machine 2 proceeding from the time point T9. Ingeneral, from the time point T9 onwards or from the time point T18onwards, the departure from the sailing operating state takes place witha simultaneous restart of the drive machine 2 and with rotational-speedcontrol, which is in turn likewise performed simultaneously, in theregion of the drive machine 2.

FIG. 6 shows the various profiles of the operating variables of thevehicle drivetrain 1 proceeding from a time point T20, which liesbetween the time points T15 and T16 as per FIG. 5 and at which thesailing operating state of the vehicle drivetrain 1 is activated. If ademand for deactivation of the sailing operating state is triggered atthe time point T20, the seventh transmission ratio “7” for forwardtravel has to be engaged in the region of the gearbox 4. The positivelyengaging shift element A is closed owing to the prevailing actuationpressure p_A. At the same time, the frictionally engaging shift elementD is also present in the closed operating state, said shift elementbeing charged with an actuation pressure p_D which is at the closingpressure level, whereas the frictionally engaging shift element C ischarged with an actuation pressure p_C which is higher, by an offsetvalue, than the pressure value pf_min plus the offset value.

With progressive operating time t, in the continued presence of anactive sailing operating state of the vehicle drivetrain 1 and in eachcase at the time points T21, T22, T23, T24 and T25, the so-calledsailing clutch logic determines through a gearspeed tracking function,which increases the spontaneity upon departure from the sailingoperating state of the vehicle drivetrain 1, that respectively the sixthtransmission ratio “6”, the fifth transmission ratio “5”, the thirdtransmission ratio “3”, the second transmission ratio “2” or the firsttransmission ratio “1” has to be engaged in the gearbox 4. Therefore, atthe time point T26, the actuation pressure p_D is lowered to the levelabove the pressure threshold pf_min+Hys plus offset value, whereas theactuation pressure p_C is raised to the closing pressure level. In thesame way, at a time point T27, which is after the time point T22, theactuation pressure p_B of the frictionally engaging shift element B isadjusted to the closing pressure level, whereas the actuation pressurep_C of the frictionally engaging shift element C is lowered to thepressure level above the pressure threshold pf_min+Hys plus the offsetvalue. At the time point T23, it is the case here that no clutch logicchange occurs, whereas, at a time point T28, which follows the timepoint T24, the actuation pressure p_C is raised to the closing pressurelevel and the actuation pressure p_B of the frictionally engaging shiftelement B is lowered to the pressure level above the pressure thresholdpf_min+Hys plus the offset value, whereby the gearbox 4 is prepared forthe engagement of the second transmission ratio “2” for forward travel.

Proceeding from a time point T29, which follows the time point T25, thegearbox 4 is prepared for the engagement of the first transmission ratio“1” for forward travel by raising the actuation pressure p_D of theshift element D to the closing pressure level, whereas the actuationpressure P_C of the frictionally engaging shift element C is lowered tothe pressure level above the pressure threshold pf_min+Hys plus theoffset value.

The latter approach results from the fact that, in the operating stateprofile of the vehicle drivetrain 1 under consideration, the vehiclespeed progressively decreases in the presence of an active sailingoperating state and it is detected through the sailing clutch logicthat, with progressive operating time t, the gearspeed that has to beengaged in the gearbox in each case upon a departure from the sailingoperating state changes and a respectively lower gear or a respectivelylower transmission ratio has to be engaged. Since, for the engagement ofthe transmission ratios “4” to “1” for forward travel, it is necessaryin each case for the further positively engaging shift element F to betransferred into the closed operating state, it is necessary beforeengagement of the transmission ratios “3” to “1” for synchronizationgears, or the synchronization transmission ratios “5”, “6” or “7”, whichcorrespond in each case to the transmission ratios “3” to “1”, to beengaged in the region of the gearbox 4.

This means that, in the presence of a demand for deactivation of thesailing operating state and for an operating state of the vehicledrivetrain to be established for this purpose, in which the thirdtransmission ratio “3” for forward travel has to be engaged in thegearbox 4, the fifth transmission ratio “5” is engaged in the gearbox 4first, and subsequently, a downshift is performed from the fifthtransmission ratio “5” towards the third transmission ratio “3”, duringwhich the further positively engaging shift element F can then likewise,with the positively engaging shift element A already closed, betransferred into its closed operating state accordingly with littleeffort.

In the event that the second transmission ratio “2” for forward travelhas to be engaged in the gearbox 4 as a result of a demand fordeactivation of the sailing operating state, first the sixthtransmission ratio “6” for forward travel is engaged in the gearbox 4,and subsequently the downshift is performed from the sixth transmissionratio “6” in the direction of the second transmission ratio “2”, duringwhich the further positively engaging shift element F is engaged inaddition to the already-closed shift element A. It is furthermoreprovided that the seventh transmission ratio “7” is engaged first in thegearbox 4, and subsequently the downshift is performed from the seventhtransmission ratio “7” in the direction of the first transmission ratio“1”, if the first transmission ratio stage “1” has to be engaged in theregion of the gearbox 4 as a result of a demand for deactivation of thesailing operating state of the vehicle drivetrain 1. Then, the furtherpositively engaging shift element F can be transferred into its closedoperating state as desired in addition to the already-closed positivelyengaging shift element A.

In the present case, at a time point T30, the demand for deactivation ofthe sailing operating state in the region of the gearbox 4 occurs, forwhich the first transmission ratio “1” for forward travel has to beengaged in the gearbox 4. In order for the further positively engagingshift element F to be transferred into its closed operating state asdesired, the frictionally engaging shift element D and the positivelyengaging shift element A are correspondingly charged, proceeding fromthe time point T29, with their actuation pressures p_D and p_A, whichare at the closing pressure level. At the time point T30, the actuationpressures p_C and p_B are reduced to zero, and the frictionally engagingshift elements C and B are transferred into their open operating state.Furthermore, the drive machine 2 is activated, whereby the profile ofthe rotational speed n_mot of the drive machine 2 increases, proceedingfrom the time point T30, in the direction of the idle rotational speedn_motLL in a manner controlled in closed-loop fashion as a function ofthe EGS engine target rotational speed setpoint.

At a time point T31, which follows the time point T30, the frictionallyengaging shift element E is charged with a fast-charging pulse during afast-charging phase and is subsequently charged with a chargingcompensation pressure during a charging compensation phase, wherein thecharging compensation phase ends in the present case at a time pointT32. Subsequently, the actuation pressure p_E is increased according toa first pressure ramp proceeding from the time point T32, whereby thesynchronization transmission ratio which corresponds to the firsttransmission ratio “1”, or the seventh transmission ratio “7”, isengaged in the gearbox 4. With further increasing actuation pressure p_Eof the frictionally engaging shift element E, the turbine rotationalspeed n_t increases in the direction of the profile n_ab*i_zielgang_sas,and corresponds to this profile at the time point T33, at which theshift element E exhibits its full torque transfer capacity. At the timepoint T33, the actuation pressure p_E of the frictionally engaging shiftelement E is in turn lowered to the level of the pressure thresholdpf_min+Hys plus the offset value in order to transfer the furtherpositively engaging shift element F as desired into an operating stateexpedient for the activation thereof. Here, a rotational speeddifference between the shift element halves of the further positivelyengaging shift element F is transferred into a rotational speeddifference window expedient for the activation of the further positivelyengaging shift element F, and the further positively engaging shiftelement F is, at a time point T34, charged with the actuation pressurep_F required for the activation and transferred into its closedoperating state.

At a time point T35 following shortly thereafter T34, it is detectedthat the further positively engaging shift element F is present in theclosed operating state, because, at the time point T35, the profile ofthe turbine rotational speed n_t corresponds to the profilen_ab*i_zielgang_sas, which in a known manner arises in the case of thefirst transmission ratio “1” being engaged in a gearbox 4. For thisreason, at the time T35, the actuation pressure p_E of the shift elementE is reduced to zero in the illustrated manner, and the frictionallyengaging shift element E is fully opened, whereby the sailing operationis deactivated and the vehicle drivetrain 1 is in the demanded operatingstate.

The approach according to the invention is particularly suitable forgear set concepts in conjunction with correspondingly designed shiftelements arranged in the gear set, in the case of which, as a result ofthe opening of a frictionally engaging shift element, the drive outputof a vehicle drivetrain can rotate independently of the gear set of thegearbox. This is, in the exemplary embodiment of the automatic gearbox 4being considered here, the shift element E. Through the further shiftelements (more specifically the brakes D and C), one shift element halfof the positively engaging shift element A (more specifically therotational speed thereof) can be set to zero. Furthermore, therotational speed of the further shift element half of the shift elementA and of the gearbox input shaft 6 can be set to zero by closing shiftelement B in the presence of an active sailing operating state of thevehicle drivetrain 1. Through this active blocking of the gear set 5,pressure level changes of the actuation pressures of the shift elementscan be performed dynamically during the above-described gearspeedtracking, and can be set as in the case of conventionally implementedoverlapping shifts.

If the shift elements B, C or D are charged with a pressure level abovethe charging pressure, such as is required for the blocking of the gearset 5, the blocking of the gear set 5 is maintained, and the turbinerotational speed n_t is equal to zero. Thus, over the entire operatingrange of the gearbox 4, fast gearspeed tracking can be implemented, andcharging of the shift elements B, C or D using an electrically driveableauxiliary pump of the gearbox 4 is not necessary. If a restart of thedrive machine 2 is demanded by a corresponding demand for deactivationof the sailing operating state, those shift elements of the gearbox 4which are respectively not required for realizing the demanded operatingstate of the vehicle drivetrain can be easily deactivated by reducingthe respective actuation pressure.

The gearspeed tracking, described in particular with regard to FIGS. 5and 6, in the presence of the active sailing operating state of thevehicle drivetrain 1 in the region of the gearbox 4 can also beimplemented in the opposite direction in the case of increasing vehiclespeed and increasing drive output speed n_ab. Such an increase in thedrive output rotational speed occurs for example when a vehicle equippedwith a vehicle drivetrain that can be operated in accordance with theinvention is traveling downhill. Furthermore, it is also possible forthe vehicle speed to be increased using a further drive of a vehiclewhich is independent of the drive machine, such as for example anelectric vehicle axle or the like.

Regardless of the event that increases the drive output speed, in theevent of a transition into the sailing operating state of the vehicledrivetrain 1 in the case of lower transmission ratios “1” to “8” forforward travel engaged in the gearbox 4, that the gear set 5 is firstlytransferred as described above into the partially blocked operatingstate by closure of the shift elements B, C and D. Subsequently, it ismonitored in each case whether a higher transmission ratio has to beengaged in the gearbox 4 than at the time point at which the sailingoperating state of the vehicle drivetrain 1 was activated in order torealize the operating state of the vehicle drivetrain 1 required for adeparture from the sailing operating state at the present operatingpoint of the vehicle drivetrain 1. If this is the case, the gearbox 4 isrespectively actuated through corresponding actuation of the shiftelements A to F as required for the purpose, and preparation is made forthe transmission ratio to be engaged in the region of the gearbox 4 in amanner dependent on the respectively present operating point of thevehicle drivetrain, in such a way that, in the event of a departure fromthe sailing operating state, the demanded operating state of the vehicledrivetrain can be realized within short operating times.

FIG. 7 to FIG. 11 show in each case several profiles of differentoperating variables of the vehicle drivetrain 1 versus the time t,wherein, at a time point T130 denoted in more detail in FIG. 7, thevehicle drivetrain 1 is in turn in a driving operating state in whichthe eighth transmission ratio “8” or the ninth transmission ratio “9”for forward travel is engaged in the gearbox 4 and a rotational speedn_mot of the drive machine 2 is higher than an idle rotational speedn_motLL of the drive machine 2. At the time point T130, a demand is madefor realizing a sailing operating state of the vehicle drivetrain 1during which the drive machine 2 is active and the power flow betweenthe drive machine 2 and the drive output 3 is interrupted in the regionof the gearbox 4. Proceeding from the time T130, the rotational speedn_mot of the drive machine 2 is adjusted increasingly towards the idlerotational speed n_motLL as illustrated. For activation of the sailingoperating state of the vehicle drivetrain 1, proceeding from the timepoint T131, the frictionally engaging shift element E is, bycorresponding lowering of the actuation pressure p_E, transferred intoits open operating state in the manner illustrated in FIG. 7 until thetime point T132, and the power flow between the drive machine 2 and thedrive output 3 is thereby disconnected in the region to gearbox 4.

The lowering of the torque transfer capacity of the frictionallyengaging shift element E has the effect that, proceeding from a timepoint T133 which lies between the time points T131 and T132, therotational speed n_t of the gearbox input shaft 6 deviates from theproduct of the rotational speed n_ab of the drive output 3 and thetransmission ratio i_zielgang_sas presently engaged in the gearbox atthe time point T130. If the deviation between the turbine rotationalspeed n_t and the product of the rotational speed n_ab multiplied by thetransmission ratio i_zielgang_sas exceeds a threshold value kfl, then inthe present case the disconnected power flow between the drive machine 2and the drive output 3 in the region of the gearbox 4 is detected. Thisoccurs in the present case at a time point T134, which lies between thetime points T133 and T132.

At the time T134, in the case of the ninth transmission ratio “9” forforward travel engaged in the gearbox 4, the actuation pressure p_C ofthe frictionally engaging shift element C is raised in abrupt fashion,in the manner illustrated in idealized fashion in FIG. 7, to the levelof the fast-charging pressure and is maintained at said level until atime point T135. Subsequently, the actuation pressure p_C is lowered, atthe time point T135, to an intermediate pressure level and is raised inramped fashion through two successive pressure ramps until a time pointT138, at which the frictionally engaging shift element C is in aslippage-free operating state. At the time point T136, the actuationpressure p_C is raised to a level at which the frictionally engagingshift element C is fully closed.

If, at the time point T130, the eighth transmission ratio “8” forforward travel is engaged in the gearbox 4, it is the case that, betweenthe time points T134 and T136, instead of the actuation pressure p_C,the actuation pressure p_B of the frictionally engaging shift element Bis adjusted in the last-described manner in order to transfer thefrictionally engaging shift element B into the closed operating state inaddition to the frictionally engaging shift elements C and D.

In the closed operating state of the frictionally engaging shiftelements C, D and B, the gear set 5 of the gearbox 4 is in a partiallyblocked operating state in which the gearbox input shaft 6 is heldrotationally fixed and the gearbox output shaft 9 connected to the driveoutput 3 is rotatable. In this operating state of the gearbox 4, anincrease of the actuation pressure p_A of the positively engaging shiftelement A occurs, whereby the positively engaging shift element A istransferred into its closed operating state. At the same time, the drivemachine 2 is operated at the idle rotational speed n_motLL.

At a time point T144, the closed operating state of the shift element Ais detected, as a result of which both the actuation pressure p_B of thefrictionally engaging shift element B and also the actuation pressurep_C of the frictionally engaging shift element C are lowered in themanner illustrated to zero at the time point T144, whereby, at the timeT144, the sailing operating state of the vehicle drivetrain 1 demandedat the time point T130 is activated as desired.

In the present case, the sailing operating state is demanded by a demandfrom a driver, for example by a release of an accelerator pedal and anactuation, preferably by the driver, of the service brake. In additionor as an alternative to this, it is also possible for the sailingoperating state to be demanded by a superordinate driving strategy if nodemand for power is made by the driver and it is additionally determinedthat a driving route, determined for example using a navigation system,can be traveled at least in sections in sailing operation with low fuelconsumption.

In the present case, in the manner shown in FIG. 7, the vehicledrivetrain 1 remains in the sailing operating state up until a timepoint T137. At the time point T137, it is for example the case that thedriver actuates the accelerator pedal again and demands a correspondinglevel of power from the drive machine 2. This demand for power from thedriver has the effect that the rotational speed n_mot of the drivemachine 2 increases proceeding from the time point T137. To prevent anuncontrolled increase of the engine rotational speed n_mot, the drivemachine 2 is operated in the closed-loop rotational speed control modeproceeding from the time point T137, and a gearbox-side engine targetrotational speed setpoint which corresponds to the profile n_motEGS isimplemented. As a result of the activation of the engine targetrotational speed setpoint, the engine rotational speed n_mot is,proceeding from the time point T137, raised to a level which lies abovethe rotational speed n_t of the gearbox input shaft 6, which emergesfrom the product of the drive output rotational speed n_ab and thetransmission ratio i_zielgang_sas to be engaged in the gearbox 4 at thetime point T137.

Since, at the time point T137, the vehicle drivetrain 1 is in anoperating state in which, in the presence of a deactivated sailingoperating state, the transmission ratio engaged in the gearbox 4 at thetime point T130 has to be engaged in the gearbox 4, that is to say theninth transmission ratio “9” or the eighth transmission ratio “8” forforward travel, the actuation pressure p_A of the positively engagingshift element A is lowered at the time point T137, and the positivelyengaging shift element A is transferred, at the time point T137, intoits open operating state. At a time point T145 which follows the timepoint T137, the open operating state of the positively engaging shiftelement A is detected, and the frictionally engaging shift element C orB is pre-charged by a fast-charging pulse which lasts until a time pointT146. At the time point T146, the actuation pressure p_C or p_B isadjusted to an intermediate pressure level, and is raised to a furtherintermediate pressure level in ramped fashion through two successivepressure ramps until a time point T147, at which the frictionallyengaging shift element C or B is in a slippage-free operating state. Atthe time point T147, the actuation pressure p_C or p_B is raised to theclosing pressure level, at which the frictionally engaging shift elementC or B is fully closed.

With increasing rotational speed n_mot of the drive machine 2, theturbine rotational speed n_t also increases and follows the profile ofthe rotational speed n_mot of the drive machine 2. Proceeding from atime point T138, the actuation pressure p_E of the frictionally engagingshift element E is prepared for the activation of the shift element E,in the manner shown in FIG. 7, during a fast-charging phase which lastsuntil a time point T139 and a charging compensation phase which followssaid fast-charging phase and which lasts until a time point T140.

At the time point T140, the frictionally engaging shift element E is inan operating state in which the torque transfer capacity of thefrictionally engaging shift element E is substantially equal to zero anda further increase in the actuation pressure p_E results in an immediateincrease of the torque transfer capacity of the frictionally engagingshift element E. Proceeding from the time point T140, the actuationpressure p_E is raised through a pressure ramp which lasts until a timepoint T141. At the time point T140, the actuation pressure p_E of thefrictionally engaging shift element E is in the present case increasedby the first pressure ramp which follows the charging compensation phaseif, for the traction operation of the vehicle drivetrain 1 underconsideration here, the value of the rotational speed n_mot of the drivemachine 2 has reached or even exceeded the profile n_ab*i_zielgang_sas,and a rotational speed difference Nd_Syn between the shift elementhalves of the shift element E to be activated is close to thesynchronous rotational speed or less than or equal to a threshold value.

By contrast to this, proceeding from the time point T140, the actuationpressure p_E of the shift element E to be activated is, in coastingoperation of the vehicle drivetrain 1 in a manner not illustrated in anymore detail, increased by the first pressure ramp which follows thecharging compensation phase if: 1) the value of the rotational speedn_mot of the drive machine 2 lies below or corresponds to the profilen_ab*i_zielgang_sas and 2) a rotational speed difference Nd_Syn betweenthe shift element halves of the shift element E to be activated is closeto the synchronous rotational speed or less than or equal to a thresholdvalue.

Subsequently the actuation pressure p_E of the frictionally engagingshift element E is increased further by a further pressure ramp, thegradient of which is smaller than that of the pressure ramp presentbetween the time points T140 and T141. At the end of the second pressureramp, that is to say in the present case at the time point T142, thefrictionally engaging shift element E is present in a slippage-freeoperating state and the turbine rotational speed n_t corresponds to theproduct of the drive output rotational speed n_ab and the transmissionratio i_zielgang_sas to be engaged in the gearbox 4 demanded at the timepoint T137, which transmission ratio in the present case correspondseither to the ninth transmission ratio “9” or the eighth transmissionratio “8”.

In this case, too, the engine rotational speed n_mot is adjusted byadjusting the gearbox-side engine target rotational speed setpoint to alevel above a current value of the profile of the productn_ab*i_zielgang_sas in order to avoid, during the establishment of thepower flow between the drive machine 2 and the drive output 3 in theregion of the gearbox 4, an undesired crossing of rotational speedsbetween the rotational speed n_mot of the drive machine 2 and theturbine rotational speed n_t, which is determined from the transmissionratio i_zielgang to be engaged in the gearbox 4 and the drive outputrotational speed n_ab.

At the time point T143, the actuation pressure p_E of the frictionallyengaging shift element E is at the closing pressure level, and theoperating state of the vehicle drivetrain 1 demanded at the time pointT137 has been established as desired at the time point T143. After thetime point T143, proceeding from which the sailing operating state ofthe vehicle drivetrain 1 has been ended, any demanded subsequent shiftscan be performed as desired in the gearbox 4.

The approach described with regard to FIG. 7, specifically the transferof the positively engaging shift element A into its closed operatingstate already at the time point T136, offers advantages with regard tothe spontaneity of the vehicle drivetrain 1 if a demand for deactivationof the sailing operating state of the vehicle drivetrain 1 demands anoperating state of the vehicle drivetrain 1 for which, in the region ofthe gearbox 4, it is necessary to engage one of the transmission ratios“7” to “1” for forward travel, for the realization of which thepositively engaging shift element A has to be transferred into or heldin its closed operating state, because said shift element is thenalready present in its closed operating state at the time point T137.

Thus, in a simple manner, a situation is avoided in which, in thepresence of high likelihood of a departure from sailing as a result of aload demand from a driver, a downshift is demanded during which thepositively engaging shift element A has to be transferred into itsclosed operating state. Long shift times and low performance after adeparture from sailing, owing to a dog-clutch downshift to be performedin accordance with a demand during a departure from sailing, are thusavoided. During the synchronization of the positively engaging shiftelement A to be activated, the converter lock-up clutch 8 is opened inorder to prevent stalling of the drive machine 2 owing to the gearboxinput shaft 6 being held rotationally fixed. Subsequently, during theactive sailing operating state, the actuation of the converter lock-upclutch 8 performed before the demand for activation of the sailingoperating state is enabled again.

As an alternative it may also be provided that the vehicle drivetrain isconfigured, in the region between the drive machine and the gearbox,with only one frictionally engaging shift element or, more specifically,one frictionally engaging clutch which is operated with open-loop and/orclosed-loop control to an extent corresponding to the actuation of theconverter lock-up clutch in order, as desired, to synchronize thepositively engaging shift element A to be activated and simultaneouslyprevent stalling of the drive machine 2.

In order to ensure the engagement of the positively engaging shiftelement A during a transition into sailing, the closing of thefrictionally engaging shift elements B, C and D provided simultaneouslyfor the closure of the positively engaging shift element A can be variedby opening the frictionally engaging shift element B in order toeliminate a tooth-on-tooth position that exists in the region of thepositively engaging shift element A, because a high torque can beimparted to the positively engaging shift element A by opening thefrictionally engaging shift element B.

It is also possible to provide, in the region of the drive machine 2, anengine torque intervention in which the rotational speed n_mot of thedrive machine 2 is increased proceeding from the idle rotational speedn_motLL in order to impart a disturbance torque which eliminates thetooth-on-tooth position in the region of the positively engaging shiftelement A. In addition or alternatively to this, it is also possible tobriefly increase the torque transfer capacity of the converter lock-upclutch 8 in order to eliminate the tooth-on-tooth position in the regionof the positively engaging shift element A by eliminating the partialblocking of the gear set 5.

By contrast to this, it is also possible for the positively engagingshift element A to be partially closed by the actuation in the closingdirection but not to reach its desired end position and thus its fullyclosed operating state. If a torque prevails at the positively engagingshift element A which prevents the complete closure of the positivelyengaging shift element A, the shift elements B, C and A continue to beactuated in the closing direction during the closing process of theshift element A, while the frictionally engaging shift element D istransferred into its closed operating state, whereby the torqueprevailing at the positively engaging shift element A is reduced to anextent which promotes the closing process, and a so-called release ofclaw load is performed.

Such torques which impair the closing process of the positively engagingshift element A result inter alia from gearbox-internal drag torques andfurther influences which subject the positively engaging shift elementA, during its closing process, to such a high torque that a completesliding-in movement is no longer possible.

The approach described above with regard to FIG. 7 of transferring thepositively engaging shift element A into its closed operating statealready during the transition into sailing offers considerableimprovements with regard to the spontaneity of the vehicle drivetrain 1during a transition into sailing proceeding from the transmission ratios“9” or “8” at vehicle speeds slower than a threshold value, becausethen, upon a departure from sailing, it is necessary in any case for alower gear to be engaged in the gearbox 4, and the departure fromsailing will in any case involve a downshift. In the presence ofrelatively high vehicle speeds, this approach may however be disturbingand disadvantageous because the positively engaging shift element A doesnot have to be transferred into the closed operating state in order torealize an operating state of the vehicle drivetrain 1 demanded as aresult of a departure from sailing. Therefore, a speed-dependentdefinition of the strategy for dog-clutch conditioning is provided inorder for the preconditioning of the positively engaging shift elementA, as described with regard to FIG. 7, during the active sailingoperating state of the vehicle drivetrain to be limited to operatingranges in which the preconditioning effects an improvement inspontaneity.

This means that, upon a transition into sailing proceeding fromoperating states in which the transmission ratio “9” or “8” for forwardtravel is engaged in the gearbox 4, the positively engaging shiftelement A is not transferred into its closed operating state if thevehicle speed is higher than the threshold value and, a present demandfor deactivation of the sailing operating state, for an operating stateof the vehicle drivetrain 1 to be realized in which the eighthtransmission ratio “8” or the ninth transmission ratio “9” for forwardtravel has to be engaged in the gearbox 4, the positively engaging shiftelement A has to be transferred into or held in the open operatingstate. Then, the positively engaging shift element A is left in its openoperating state at the time point T136 and, by contrast to the operatingstate of the vehicle drivetrain 1 as per FIG. 7, said positivelyengaging shift element A does not have to be transferred into its openoperating state at the time point T137.

This approach has advantages in relation to the approach discussed withregard to FIG. 7. First, at the time point T136, in the gearbox 4, it isnot necessary for any present tooth-on-tooth positions in the region ofthe positively engaging shift element A owing to the partially blockedoperating state of the gear set 5 to first be eliminated bycorresponding variation of the torque transfer capacity of one of thethree simultaneously closed shift elements C, D or B. Further, in theregion of the positively engaging shift element A, it is not necessaryfor a rotational speed difference expedient for the activation thereofto be established between shift element halves of the positivelyengaging shift element A. Furthermore, any present bracing states in theregion of the positively engaging shift element A at the time pointT137, at which the positively engaging shift element A is transferredinto its open operating state during the operating state profile basedon FIG. 7, do not have to be eliminated by corresponding changing of thetorque transfer capacity of the shift element C or B which thenadditionally has to be deactivated before the positively engaging shiftelement A can be transferred into its open operating state in order torealize the ninth transmission ratio “9” or the eighth transmissionratio “8” for forward travel.

Furthermore, the actuation of the frictionally engaging shift element E,which has to be transferred into its closed operating state in order toestablish the power flow between the drive machine 2 and the driveoutput 3, can, from as early as the time point T137, at which the demandfor deactivation of the sailing operating state of the vehicledrivetrain 1 is triggered, be transferred into its closed operatingstate with greater spontaneity than is possible during the operatingstate profile of the vehicle drivetrain 1 based on FIG. 7.

If the vehicle drivetrain 1 is in sailing operation and if the gearbox 4is operated over relatively long operating periods in accordance withthe second variant of the shift logic such that the positively engagingshift element A is already activated and the shift element E isadditionally held in the closed operating state, excessively high dragtorques are permanently generated in the gearbox 4 during constantdriving operation. Therefore, after a defined operating time haselapsed, the gearbox 4 is operated in accordance with the first variantof the shift logic. Here, the present gradient of the rotational speedn_ab of the drive output 3 constitutes in each case a decision criterionas regards whether, in the presence of an active sailing operating stateof the vehicle drivetrain 1, the gearbox 4 is operated permanently inaccordance with the first variant or in accordance with the secondvariant of the shift logic.

If (1) the vehicle drivetrain 1 is in the sailing operating state in thepresence of a drive output rotational speed n_ab at which the eighthtransmission ratio “8” or the ninth transmission ratio “9” has to beengaged in the gearbox 4 upon a departure from the sailing operatingstate, (2) the gearbox 4 is actuated in accordance with the firstvariant or the second variant of the shift logic, and (3) both thepositively engaging shift element A and the frictionally engaging shiftelement E are present in the closed operating state, then, in thepresence of a demand for realization of a neutral operating state of thegearbox 4 for which the positively engaging shift element A has to beheld in or transferred into the open operating state, a gearspeed jumpin the direction of the seventh transmission ratio “7” is performed bysoftware before the realization of the neutral operating state. Thus, ina simple manner, the neutral operating state of the gearbox 4 isimplemented in accordance with a demand in the presence of asimultaneously engaged positively engaging shift element A.

This offers the advantage that the new shift logic, during which thepositively engaging shift element A is preconditioned in the sailingoperating state of the vehicle drivetrain 1, can, for the case of ademanded gear disengagement process which is assigned the highestpriority, be implemented without a new shift sequence, and additionalhardware resources are not required. Using this approach, existing shiftsequences remain possible with little outlay, and gear disengagementsequences can be implemented with high spontaneity, because the powertransmission in the region of the gearbox 4 is already fully completelyreduced before the positively engaging shift element A is transferredinto its open operating state.

FIG. 8 shows the profiles of the operating variables of the vehicledrivetrain 1 as per FIG. 7 during an operating state profile of thevehicle drivetrain 1 after the time point T136, at which the vehicledrivetrain 1 is already present in the sailing operating state. At atime point T148, the gearbox 4 is in an operating state for which, inthe gearbox 4, only the positively engaging shift element A is closed,whereas all other shift elements B to F are open. Up to a time pointT149, a superordinate driving strategy identifies that, in the event ofa possible departure from the sailing operating state of the vehicledrivetrain 1, the seventh transmission ratio “7” for forward travel hasto be engaged in the gearbox 4. At the time point T149, the drivingstrategy determines, in the presence of an active sailing operatingstate of the vehicle drivetrain 1 and in a manner dependent on thepresent operating state profile of the vehicle drivetrain 1, that, inthe event of a departure from the sailing operating state, the sixthtransmission ratio “6” for forward travel, or in the case of anoperating state profile which deviates from this, the fifth transmissionratio “5” for forward travel, has to be engaged in the gearbox 4.

Owing to the fact that the driving strategy has identified that thesixth transmission ratio “6” or the fifth transmission ratio “5” forforward travel has to be engaged in the gearbox 4 proceeding from thetime point T149, it is provided, in order to increase the spontaneity ofthe gearbox 4, that either the actuation pressure p_C of thefrictionally engaging shift element C or the actuation pressure p_B ofthe frictionally engaging shift element B is, at the time point T149,increased to the fast-charging pressure level of the shift element C orB respectively and is, at a subsequent time point T150, reduced to thelevel of the charging compensation pressure, and is maintained at saidpressure over a period until a time point T151, which in the presentcase represents the end of the charging compensation phase of the shiftelement C or B. Subsequently the actuation pressure p_C or p_B of theshift element C or B respectively is increased by three successivepressure ramps until a time point T152 to a pressure level at which thefrictionally engaging shift element C or B is present in the closedoperating state, wherein, at the time point T152, the actuation pressurep_C or p_B respectively is increased to the closing pressure level. Withprogressive operating time t, the drive output rotational speed n_ab andthus the profile of the product n_ab*i_zielgang_sas decreasecontinuously to the extent illustrated.

If the gearbox 4 is operated in accordance with the standard sailinglogic, the superordinate driving strategy determines after the timepoint T152, that, in addition to the positively engaging shift elementA, the further positively engaging shift element F also has to betransferred into its closed operating state in order to be able toengage one of the transmission ratios “1” to “4” of the firsttransmission ratio subrange in the gearbox 4 with high spontaneity inthe event of a departure from sailing.

In the presence of simultaneously closed shift elements A and B, therotational speed difference dnF between the shift element halves of thefurther positively engaging shift element F can be determined using thefollowing relationship, expressed below in the form of a formula:dnF=X*n_t+Y*n_ab

Here, the variables X and Y represent factors which are dependent on therespective transmission ratios of the individual gear sets of thegearbox 4. In the presence of simultaneously active shift elements A andB, it is the case in the exemplary embodiment of the gearbox 4 as perFIG. 1, as is considered here, that the variable X has a value equal to−1.1, whereas Y is equal to −2.1. By contrast to this, in the presenceof simultaneously active shift elements A and C, X is equal to −0.739,while Y is again equal to −2.1.

In the present case, using the relationship according to the formula, atthe time T153 a rotational speed difference value between the shiftelement halves of the further positively engaging shift element F whichis expedient for the closure of the further positively engaging shiftelement F is determined and the further positively engaging shiftelement F is transferred into its closed operating state by acorresponding increase of the actuation pressure p_F of the furtherpositively engaging shift element F. At the same time, the actuationpressure p_C or p_B of the frictionally engaging shift element C or Brespectively is, proceeding from the time point T153, reduced to theextent illustrated in FIG. 8, and is reduced to zero until a time pointT154. The activation of the further positively engaging shift element Fand the subsequent deactivation of the frictionally engaging shiftelement C or B respectively has the effect that the turbine rotationalspeed n_t initially follows the profile of the productn_ab*i_zielgang_sas and, proceeding from the time point T154, returns inthe direction of the engine rotational speed n_mot.

Thus, the change from the second transmission ratio subrange towards thefirst transmission ratio subrange of the gearbox 4 is implemented in asimple manner without additional measures in the presence of the stillactive sailing operating state of the vehicle drivetrain 1. Withprogressive operating time t, proceeding from the operating state of thevehicle drivetrain 1 that is present at the time point T154, a continuedsailing operating state with decreasing drive output rotational speedn_ab can be implemented without further actuation of the gearbox 4 andcan additionally be deactivated with high spontaneity because a possiblyrequired build-up of power transmission in the region of the gearbox 4between the drive machine 2 and the drive output 3 can then be realizedby activation of the frictionally engaging shift element B, C or D,without additional actuation of the positively engaging shift elements Aand F within short operating times.

In the present case, such a demand is triggered at the time point T155,proceeding from which the actuation pressure p_C or p_B of thefrictionally engaging shift element C or B respectively is initially setas illustrated, via a fast-charging phase and a subsequent chargingcompensation phase until a time point T156, for an activation of theshift element C or B respectively. Following the time point T156 theactuation pressure p_C or p_B is increased for example by threesuccessive pressure ramps until a time point T157 to a level at whichthe frictionally engaging shift element C or B is present in theslippage-free operating state, and the actuation pressure p_C or p_B isincreased, at the time point T157, to the closing pressure level of thefrictionally engaging shift element C or B respectively.

As an alternative to this, it is also possible for a vehicle equippedwith the vehicle drivetrain 1 to coast to standstill proceeding from thetime point T155, and for the vehicle drivetrain 1 to be operated inaccordance with an engine start-stop function, and for the twopositively engaging shift elements A and F to be activated and for thefurther shift elements C, D, B and E to be present in the open state inthe gearbox 4, when the vehicle is in the standstill state or alreadyclose to the standstill state. When the vehicle is at a standstill, thedrive machine 2 which is decoupled from the drive output 3 is shut down,and in the event of a corresponding demand for launching the vehicle,said drive machine 2 is started and the shift element D, C, B or E thathas to be activated in each case for realizing the demanded startingtransmission ratio “1”, “2”, “3” or “4” for forward travel istransferred into the closed operating state.

The above-described gearspeed tracking of the further positivelyengaging shift element F is performed in the presence of virtuallyconstant rotational speeds n_mot and n_t of the drive machine 2 and ofthe gearbox input shaft 6 in the presence of simultaneously varyingrotational speed n_ab of the drive output 3, whereby the furtherpositively engaging shift element F reaches its synchronous state. Toavoid reaction torques in the vehicle drivetrain 1 that are perceptibleto a driver, after the closure of the further positively engaging shiftelement F the previously actuated shift element C or B is deactivated.

The use of the further positively engaging shift element F as aforce-closing clutch is possible owing to the virtually load-freeoperating state of the further positively engaging shift element F,which in turn results from the low torque transmitted via thehydrodynamic torque converter 7 in the presence of a simultaneously openconverter lock-up clutch 8. During the determination of thesynchronization point of the further positively engaging shift element Fto be activated, the torque transfer capacity of the converter lock-upclutch 8 is set such that the rotational speeds n_mot and n_t of thedrive machine 2 and of the gearbox input shaft 6 correspond to eachother and so as to transfer the further positively engaging shiftelement F into an operating state expedient for its activation.

FIG. 9 shows the profiles of the operating variables of the vehicledrivetrain 1 as per FIG. 7 and FIG. 8 during an operating state profileof the vehicle drivetrain 1 in which, in the region of the gearbox 4, ata time point T158, the seventh transmission ratio “7” for forward travelis engaged and the drive machine 2 is active. At the time point T158,the rotational speed n_mot of the drive machine 2 is higher than theidle rotational speed n_motLL of the drive machine 2, and a demand istriggered for realizing the sailing operating state of the vehicledrivetrain 1 during which the drive machine 2 is active and the powerflow between the drive machine 2 and the drive output 3 is disconnectedin the region of the gearbox 4. Proceeding from a time point T159, thefrictionally engaging shift element E is transferred, to the same extentas following the time point T131, into its open operating state. In thepresent case, the frictionally engaging shift element E reaches the openoperating state at the time point T160. The engine rotational speedn_mot is reduced towards the idle rotational speed n_motLL and reachesthe latter likewise at the time point T160. Owing to the openfrictionally engaging shift element E, the power transmission betweenthe drive machine 2 and the drive output 3 is disconnected in the regionof the gearbox 4, whereby the turbine rotational speed n_t alsodecreases towards the idle rotational speed n_mot.

With progressive operating time t, the superordinate driving strategyidentifies that, at a time point T161, the vehicle drivetrain 1 ispresent in an operating state in which the sixth transmission ratio “6”or the fifth transmission ratio “5” for forward travel has to be engagedin the region of the gearbox 4 in the event of a demand for deactivationof the sailing operating state. For this reason, the actuation pressurep_D of the frictionally engaging shift element D is reduced abruptlyfrom the closing pressure level to an intermediate pressure level at thetime point T161, is subsequently reduced in continuous fashion along apressure ramp until a time point T162, and is reduced to zero at thetime point T162. At the time point T161, the actuation pressure p_C orp_B of the frictionally engaging shift element C or B respectively isincreased to the fast-charging pressure level and, at a subsequent timepoint T163, is reduced to the level of the charging compensationpressure at which the actuation pressure p_C or p_B is maintained untila time point T164.

The time point T164 constitutes the end of the charging compensationphase of the frictionally engaging shift element C or B respectively.Proceeding from the time point T164, the actuation pressure p_C or p_Bof the frictionally engaging shift element C or B respectively is inturn increased for example by three successive pressure ramps until thetime point T162 to a pressure level at which the frictionally engagingshift element C or B respectively is in the slippage-free operatingstate. At the time point T162, the actuation pressure p_C or p_B isincreased to the closing pressure level, whereby the frictionallyengaging shift element C or B is, in addition to the positively engagingshift element A, present in the closed operating state. Proceeding fromthe time point T162, in the gearbox 4, a change from the operating stateof the gearbox 4 prepared for the activation of the fifth transmissionratio “5” for forward travel towards the operating state of the gearbox4 prepared for the activation of the fourth transmission ratio “4” isperformed by software without a change in the clutch logic beingperformed for this purpose.

At the time T165, it is identified by the superordinate driving strategythat, in the event of a departure from the sailing operation of thevehicle drivetrain 1, the second transmission ratio “2” for forwardtravel has to be engaged in the region of the gearbox 4, for whichreason the actuation pressure p_B of the frictionally engaging shiftelement B is, at the time point T165, reduced to an intermediatepressure level at which the frictionally engaging shift element B istransferred into slipping operation. At the same time, the actuationpressure p_C of the frictionally engaging shift element C is increasedto the level of the fast-charging pressure and is maintained at saidlevel until a time point T166. The actuation pressure p_B of thefrictionally engaging shift element B is reduced in continuous fashionalong a pressure ramp from the time point T165 to the time point T167.The actuation pressure p_C is, after ending of the charging compensationphase, which in the present case ends at the time point T168, increasedduring two subsequent pressure ramps until the time point T167 to apressure level at which the frictionally engaging shift element C ispresent in a slippage-free operating state. For this reason, theactuation pressure p_C is increased to the closing pressure level at thetime point T167, while the actuation pressure p_B is reduced to zero atthe time point T167.

At a time point T169, the superordinate driving strategy identifies anoperating state of the vehicle drivetrain in which, in the event of adeactivation of the sailing operating state, the first transmissionratio “1” for forward travel has to be engaged in the gearbox 4.Therefore, at the time point T169, the frictionally engaging shiftelement p_C is deactivated in the same manner as the frictionallyengaging shift element B was previously disengaged between the timepoints T165 and T170, and the frictionally engaging shift element D is,between the time points T169 and T170, transferred by a fast-chargingphase, a subsequent charging compensation phase, and a pressure rampinto its slippage-free operating state and, at the time point T170,transferred into its fully closed operating state.

Thus, at the time point T170, both the shift element A and the shiftelement D are closed in the gearbox 4. At a time point T171 followingthe time point T170, a demand for deactivation of the sailing operatingstate and for coupling-on of the drive machine 2 is triggered.Proceeding from the time point T171, the drive machine 2 is in turn inthe closed-loop rotational speed control mode, and the engine rotationalspeed n_mot is in turn increased in accordance with the EGS enginetarget rotational speed setpoint until the engine rotational speed n_motis equal to the profile of the product n_ab*i_zielgang_sas at the timepoint T172. In this operating state, the further positively engagingshift element F is present in its synchronized operating state, forwhich reason the actuation pressure p_F of the further positivelyengaging shift element F is increased to the extent illustrated in FIG.5 and the further positively engaging shift element F is transferred asrequired into its closed operating state, whereby the first transmissionratio “1” for forward travel is engaged in the gearbox 4. Theclosed-loop rotational speed control mode of the drive machine 2 is inthe present case ended at the time point T173, whereby the sailingoperating state of the vehicle drivetrain 1 is deactivated andsubsequent shifts in the gearbox 4 can be performed using conventionalshift processes in a manner dependent on the operating state.

The activation time point of the further positively engaging shiftelement F to be activated is calculated, in a manner dependent on aso-called switching time lead calculation, from the gradient of therotational speed n_mot of the drive machine 2, wherein the activation ofthe positively engaging shift element F is started at a time point atwhich the engine rotational speed n_mot is greater than or equal to theprofile of the product n_ab*i_zielgang_sas, and the rotational speeddifference in the region of the open further positively engaging shiftelement F is lower than a threshold value. In the case of the operatingstate profile described with regard to FIG. 9, the claw-type shiftelement F can be easily transferred into its synchronized operatingstate by variation of the engine rotational speed n_mot.

If, during the sequence for the activation of the further positivelyengaging shift element F, as described with regard to FIG. 8, the driveoutput rotational speed changes n_ab with such a gradient that thesynchronization point of the further positively engaging shift element Fcannot be achieved or set as required with the present operating stateof the gearbox 4, provision is made for the clutch logic to be changedat an early point in time and, in addition to the positively engagingshift element A, for the frictionally engaging shift element C or thefrictionally engaging shift element D rather than the shift element B tobe engaged in preparatory fashion in the gearbox 4 in order, in the casewhere the drive machine 2 is simultaneously operated at the idlerotational speed level, to achieve a rotational speed difference of atleast approximately zero in the region of the further positivelyengaging shift element F to be activated.

In the sequence described with regard to FIG. 8, during which thatoperating state of the vehicle drivetrain 1 in which the turbinesynchronous rotational speed of the desired synchronization gearspeedcorresponds to the engine idle rotational speed n_motLL is awaited, itis achieved by an adaptation of the synchronization gearspeed and anassociated selection of a suitable rotational speed window within whichthe positively engaging shift element F is present in each case in itssynchronized operating state that a situation in which said rotationalspeed window is missed in the event of freewheeling of the vehicle andan occurrence of a brief action on the drive output 3 is avoided.

However, if the synchronization point of the positively engaging shiftelement F cannot be attained as described in each case with regard toFIG. 8 and FIG. 9 owing to the respectively prevailing profile of therotational speed n_ab of the drive output 3 and/or the profile of theengine rotational speed n_mot of the drive machine 2 or if thesynchronization point of the further positively engaging shift element Fto be activated can be attained using one of the two approaches as perFIG. 8 or FIG. 9 only after undesirably long operating times haveelapsed, then the approaches described in more detail below on the basisof the illustrations of FIG. 10 and FIG. 11 are implemented.

At a time point T174, the sailing operating state of the vehicledrivetrain 1 is active and only the positively engaging shift element Ais closed. The engine rotational speed n_mot corresponds to the idlerotational speed n_motLL. Owing to the power transmission between thedrive machine 2 and the drive output 3 being disconnected in the regionof the gearbox 4, the turbine rotational speed n_t is equal to theengine rotational speed n_mot. The value of the productn_ab*i_zielgang_sas is higher than the idle rotational speed n_motLL anddecreases with a defined gradient. At the time point T175, thesuperordinate driving strategy identifies that, in the event of adeparture from sailing, the sixth transmission ratio “6” or the fifthtransmission ratio “5” for forward travel has to be engaged in thegearbox 4.

For this reason, at the time point T175, the actuation pressure p_C orp_B of the frictionally engaging shift element C or B respectively isset, by a fast-charging phase which lasts until a time point T176 and asubsequent charging compensation phase which follows said fast-chargingphase and which ends at the time point T177, for the activation of theshift element C or B respectively. Proceeding from the time point T177,the actuation pressure p_C or p_B is increased by three successivepressure ramps until the time point T178 to the pressure level at whichthe frictionally engaging shift element C or B respectively is presentin the slippage-free operating state. Subsequently, the actuationpressure p_C or p_B is adjusted to its closing pressure level at thetime point T178, and the frictionally engaging shift element C or Brespectively is present in the fully closed operating state. The driveoutput rotational speed n_ab and thus also the profile of the productn_ab*i_zielgang_sas decrease with a steep gradient proceeding from thetime point T178 owing to an intense deceleration of the vehicle, whichresults for example from an actuation of the service brake by thedriver.

Depending on the presently selected clutch logic the rotational speeddifference of the positively engaging shift element F to be activated isdetermined according to the relationship expressed as a formula above,and here, it is identified that the further positively engaging shiftelement F cannot be transferable into its closed operating state usingthe approach described with regard to FIG. 8 or the approach describedwith regard to FIG. 9. For this reason, the actuation pressure p_E ofthe shift element E is increased to the fast-charging pressure at thetime point T179 and decreased to the charging compensation pressurelevel at the time point T180. The charging compensation phase of thefrictionally engaging shift element E ends, in the present case, at forexample the time point T181. Subsequently the actuation pressure p_E isincreased with a steep gradient to an intermediate pressure level duringa first pressure ramp, and is increased further during a furtherpressure ramp which, proceeding from the time point T182, follows thefirst pressure ramp and has a gradient shallower than the gradient ofthe first pressure ramp which ends at the time point T182.

At the time T183, the frictionally engaging shift element E has a torquetransfer capacity for which, owing to the positively engaging shiftelement A already being present in the closed operating state and thefrictionally engaging shift element C or B likewise being active, thesixth transmission ratio “6” or the fifth transmission ratio “5” forforward travel is at least partially engaged in the gearbox 4.Proceeding from this operating state of the vehicle drivetrain 1, inwhich the turbine rotational speed n_t at least briefly corresponds tothe value of the product n_ab*i_zielgang_sas, the torque transfercapacity of the frictionally engaging shift element E is varied by acorresponding adjustment of the actuation pressure p_E such that theprofile of the turbine rotational speed n_t and the profile of theproduct n_ab*i_zielgang_sas at least approximately correspond to oneanother over a relatively long operating time and the further positivelyengaging shift element F to be activated exhibits its synchronizedoperating state at the time point T184. For this reason, the actuationpressure p_F of the further positively engaging shift element F isincreased at the time point T184, and a downshift is performed in thegearbox 4 proceeding from the sixth transmission ratio “6” or from thefifth transmission ratio “5” for forward travel towards the thirdtransmission ratio “3” or towards the second transmission ratio “2”,whereby the further positively engaging shift element F is transferredinto the demanded closed operating state.

To be able to activate the further positively engaging shift element Fas required for a high level of driving comfort, it is possible for theactuation pressure p_E of the frictionally engaging shift element E tobe increased slightly to the extent illustrated in FIG. 6,correspondingly to the dashed line, proceeding from a time point T185,and for the torque transfer capacity of the frictionally engaging shiftelement E to be increased. With this measure, the gradient of theturbine rotational speed n_t is reduced, and the rotational speeddifference of the positively engaging shift element F is, over arelatively long time period, kept within a rotational speed differencewindow required for the activation of the further positively engagingshift element F.

A load demand from the driver may possibly also have the effect that thesynchronization point of the further positively engaging shift element Fto be activated is not attained as described with regard FIG. 8 and FIG.9. To nevertheless be able to transfer the positively engaging shiftelement F into its activated operating state with high spontaneity asrequired, the approach described below with regard to FIG. 11 isimplemented in the event of a corresponding load demand from the driver.

At the time point T186, it is in turn the case that the sailingoperating state of the vehicle drivetrain 1 is active and only thepositively engaging shift element A is present in the closed operatingstate. The turbine rotational speed n_t and the engine rotational speedn_mot correspond to one another owing to the power transmission betweenthe drive machine 2 and the drive output 3 being disconnected in theregion of the gearbox 4. The engine rotational speed n_mot is equal tothe idle rotational speed n_motLL, while the drive output rotationalspeed n_ab is at a level such that the product of the drive outputrotational speed n_ab and the transmission ratio i_zielgang_sas isgreater than the engine idle rotational speed n_motLL.

In turn, at the time point T187, the superordinate driving strategydetermines, as a function of the present operating state profile of thevehicle drivetrain 1, that the sixth transmission ratio “6” or the fifthtransmission ratio “5” or the third transmission ratio “3” for forwardtravel has to be engaged in the gearbox in the event of a demand fordeactivation of the sailing operating state in the gearbox 4. This hasthe effect that the actuation pressure p_C or p_B of the frictionallyengaging shift element C or B respectively is set, during afast-charging phase and a subsequent charging compensation phase, whichin the present case ends at the time point T188, for the activation ofthe frictionally engaging shift element C or B respectively. Proceedingfrom the time point T188, the actuation pressure p_C or p_B is increasedduring three successive pressure ramps until the time point T189 to apressure level at which the frictionally engaging shift element C or Brespectively is present in the slippage-free operating state.

At the time point T189, the actuation pressure p_C or p_B, respectively,is increased to the closing pressure level and the frictionally engagingshift element C or B respectively is, in addition to the shift elementA, transferred into its closed operating state. At a time point T190which follows the time point T189, a load demand is made by a driver,which causes an increase in engine rotational speed n_mot proceedingfrom the idle rotational speed n_motLL. As a function of the gradient ofthe engine rotational speed n_mot, it is identified that an activationof the further positively engaging shift element F cannot be performedwithout further measures because the profile of the engine rotationalspeed n_mot intersects the profile of the product n_ab*i_zielgang_sas ata large angle, and an actuation of the further positively engaging shiftelement F in a closing direction does not result in the desiredactivation of the positively engaging shift element F.

For this reason, at the time point T190, the actuation pressure p_E ofthe frictionally engaging shift element E is increased to the level ofthe fast-charging pressure and is reduced to the charging compensationlevel at the time point T191. At the time point T192, the chargingcompensation phase is ended and the actuation pressure p_E is increasedup to a first pressure ramp ending at the time point T193 and through asecond pressure ramp which extends to the time point T194 to a pressurelevel at which the frictionally engaging shift element E exhibits atorque transfer capacity such that the sixth transmission ratio “6” orthe fifth transmission ratio “5” is at least partially engaged in thegearbox 4. The gradient of the second pressure ramp is shallower thanthe gradient of the first pressure ramp which ends at the time pointT193. Following this, the actuation pressure p_E of the frictionallyengaging shift element E is reduced along a steep pressure rampproceeding from a time point T195, the steep pressure ramp ending at thetime point T196. Proceeding from the time point T196 the actuationpressure p_E is reduced slightly along a further pressure ramp with ashallow gradient until a time point T197. This actuation of thefrictionally engaging shift element E in turn has the effect that, up toa time point T198 which precedes the time point T197, the turbinerotational speed n_t adjusts with the profile of the productn_ab*i_zielgang_sas, and the further positively engaging shift element Fto be activated is present at its synchronization point and can betransferred into its closed operating state through an increase of theactuation pressure p_F.

In order that, in turn, the further positively engaging shift element Fcan be activated with high comfort, it is possible for the actuationpressure p_F to be temporarily increased slightly proceeding from a timepoint T199 as described above with regard to FIG. 10 in order to set orflatten the gradient of the profile of the turbine rotational speed n_tto an extent that promotes the activation process of the furtherpositively engaging shift element F.

FIG. 12 shows multiple profiles of different operating variables of thevehicle drivetrain 1 versus the time t. At a time point T70 indicated inmore detail in FIG. 12, the vehicle drivetrain 1 is in a sailingoperating state in which the rotational speed n_mot of the drive machine2 is equal to zero and the power flow between the drive machine 2 andthe drive output 3 is disconnected in the region of the gearbox 4. Thevalue of the product of the rotational speed n_ab of the drive output 3and the transmission ratio i_zielgang_sas, which corresponds to atransmission ratio identified by a superordinate driving strategy as afunction of the present operating state and which is to be engaged inthe gearbox 4 upon a departure from sailing or which is equal to thetransmission ratio presently engaged in the region of the gearbox 4 inthe power flow, produced in the region of the gearbox 4, between thedrive machine 2 and the drive output 3, is greater than 0 and lower thanthe idle rotational speed n_motLL of the drive machine 2. Here, theprofile of the product n_ab*i_zielgang_sas decreases, as illustrated inmore detail in FIG. 12, with a steep gradient towards 0 over theoperating time t.

At the time T70, in the gearbox 4, the positively engaging shift elementA is initially closed, wherein the positively engaging shift element Ais, for this purpose, actuated in a closing direction with an actuationpressure p_A at a closing pressure level. Furthermore, it is also thecase that the frictionally engaging shift element C is present in aclosed operating state at the time point T70 and is, for this purpose,likewise actuated in a closing direction with an actuation pressure p_Cat the closing pressure level. The further frictionally engaging shiftelement E is fully open, because the actuation pressure p_E that can beapplied to the frictionally engaging shift element E is equal to zero.Furthermore, the frictionally engaging shift element B is charged withan actuation pressure p_B at a pressure level which is higher, by anoffset value, than the pressure value pf_min+Hys plus an offset valuedependent on a hysteresis, which constitutes an actuation thresholdabove which the frictionally engaging shift elements B, C and D are in aslippage-free operating state in the presence of an active coastingoperating state. The further shift element F is likewise charged with anactuation pressure p_F, as a result of which the further shift element Fis likewise open.

Owing to the drive machine 2 being in a shut-down state and the powerflow being disconnected in the region of the gearbox 4, the turbinerotational speed n_t is equal to zero. Said operating state of thegearbox 4 also results from the fact that, in addition to thefrictionally engaging shift elements B and C, the frictionally engagingshift element D is charged with an actuation pressure p_D which liesabove the pressure value pf_min+Hys.

At a time point T71, a pressure ramp of the actuation pressure p_D ofthe frictionally engaging shift element D ends and the frictionallyengaging shift element D is present in a slippage-free operating state.To be able, at the time point T71, to transfer the gearbox 4 into anoperating state in which not only the positively engaging shift elementA but also the frictionally engaging shift element D is fully closed inthe gearbox 4, the actuation pressure p_D is increased abruptly from theintermediate pressure level to the closing pressure level at the timepoint T71. Substantially at the same time, the actuation pressure p_C ofthe frictionally engaging shift element C is reduced from the closingpressure level to a pressure level which is higher, by an offset value,than the pressure value pf_min+Hys, at which, as before, thefrictionally engaging shift element C is in a slippage-free operatingstate. With progressive operating time t, the superordinate drivingstrategy identifies that the drive output rotational speed n_ab isdecreasing towards zero and the vehicle is transitioning to a standstillstate.

In order that the vehicle equipped with the vehicle drivetrain 1 iscapable of launching with desired high spontaneity from a standstillstate of the vehicle in the event of a corresponding demand from thedriver, a demand for activation of an engine start-stop function istriggered at a time point T72, whereby, at the same time, the sailingoperating function of the vehicle drivetrain 1 is deactivated and ademand zielgang_sas=“1” is triggered to prepare the gearbox 4 foractivation of the first transmission ratio “1” for forward travel. Theactivation of the engine start-stop function has the effect that, as afunction of the gradient of the profile of the productn_ab*i_zielgang_sas, a synchronization point of the further positivelyengaging shift element F is identified, which is to be transferred intoits closed operating state in addition to the positively engaging shiftelement A owing to the active engine start-stop function.

In the present case, it is identified that the further positivelyengaging shift element F attains its synchronization point, which isrequired for the activation, at the time point T73, as a result of whichthe actuation pressure p_F of the shift element F is increased abruptlyto the closing pressure level at the time point T73. At the time pointT73, the actuation pressure p_D of the frictionally engaging shiftelement D is reduced to a pressure level which is higher, by an offsetvalue, than the pressure value pf_min+Hys. At a time point T74, theprofile of the product n_ab*i_zielgang_sas is equal to zero, and thevehicle is at a standstill. At the same time, at the time point T74, theclosed operating state of the shift element F is identified. Up to atime point T75, the vehicle is at a standstill with the enginestart-stop function active and the drive machine 2 is in a shut-downoperating state. For this reason, the shift elements A to F are actuatedor charged with those pressure levels of the actuation pressures p_A top_F which prevail at the time point T74. At the time point T75, a demandfor starting of the drive machine 2 and for coupling the drive machine 2to the drive output 3 is triggered. For this reason, the enginerotational speed n_mot increases as illustrated towards the idlerotational speed n_motLL.

Depending on the transmission ratio “1”, “2” or “3” for forward travelto be engaged in the gearbox 4 in each case, either the actuationpressure p_D, p_C or p_B of the frictionally engaging shift element D, Cor B is increased as illustrated in FIG. 3 proceeding from the timepoint T75 until a time point T76, initially to an intermediate pressureat which the frictionally engaging shift element D, C or B is present inthe closed operating state. When the intermediate pressure level isreached at the time point T76, the actuation pressure p_D, p_C or p_B isincreased abruptly to the closing pressure level, whereby, in thegearbox 4, in addition to the two positively engaging shift elements Aand F, the frictionally engaging shift element D, C or B is additionallyactivated, and the transmission ratio “1”, “2” or “3” is engaged in thegearbox 4.

So as not to impair the starting process of the drive machine 2, it isprovided that, at the time point T75, as a function of the transmissionratio “1”, “2” or “3” to be engaged in the gearbox 4 in each case, theactuation pressures p_B and p_C, p_B and p_D or p_C and p_D are reducedfrom the pressure level above the pressure value pf_min+Hys to zero,whereby the partially blocked state of the gear set 5 of the gearbox 4,in which the gearbox input shaft 6 is held rotationally fixed, iseliminated. With increasing engine rotational speed n_mot, the turbinerotational speed n_t also increases, proceeding from the time point T75,over the operating time t. Furthermore, the profile of the productn_ab*i_zielgang_sas also increases proceeding from a time point T77,wherein the turbine rotational speed n_t lies above the profile of theproduct n_ab*i_zielgang_sas. The deviation between the turbinerotational speed n_t and the value of the product n_ab*i_zielgang_sasresults from slippage modulation in the region of the frictionallyengaging shift element D, C or B to be engaged, and this modulationallows an improvement of drivetrain comfort during engine starting ofthe drive machine 2 to be achieved. At a time point T78, the turbinerotational speed n_t is equal to the profile of the productn_ab*i_zielgang_sas because the frictionally engaging shift element D, Cor B to be activated is already in its slippage-free operating state.

Proceeding from a time point T79, in a manner dependent on therespectively present demand from the driver, the engine rotational speedn_mot remains at the level of the idle rotational speed n_motLL orincreases for example progressively further in accordance with thedashed profile of the engine rotational speed n_mot1.

FIG. 13 shows the profiles of the operating variables of the vehicledrivetrain 1 illustrated in FIG. 12 proceeding from the time point T70during an operating state profile of the vehicle drivetrain 1 duringwhich it is identified, at the time point T74, that the positivelyengaging shift element F is not transferred as required into its closedoperating state as a result of the increase of the actuation pressurep_F. For this reason, at a further time point T80 which follows the timepoint T74, the actuation pressure p_F of the positively engaging shiftelement F is reduced to zero again. Independently of this, proceedingfrom the time point T74, the engine start-stop function is activated,and the sailing operating function of the vehicle drivetrain 1 isdeactivated.

As a function of the transmission ratio “1”, “2” or “3” for forwardtravel to be engaged in the gearbox 4 upon a restart of the drivemachine 2, it is provided that either the actuation pressure p_D, p_C orp_B of the frictionally engaging shift element D, C or B is increasedfrom the pressure level above the pressure value pf_min+Hys to theclosing pressure level at the time point T80, while the actuationpressures p_B and p_C, p_B and p_D or p_C and p_D of the frictionallyengaging shift elements B and C or B and D or C and D are reduced tozero.

Since, proceeding from the time point T74, the vehicle equipped with thevehicle drivetrain 1 is at a standstill and the profile of the productn_ab*i_zielgang_sas is equal to zero, the synchronization point of thepositively engaging shift element F to be activated can no longer beattained as illustrated with regard to FIG. 12 proceeding from the timepoint T73 and the positively engaging shift element F cannot betransferred as desired into its closed operating state.

In order that, upon a restart of the drive machine 2, the transmissionratio “1”, “2” or “3” to be engaged in each case can be engaged withhigh spontaneity in the gearbox 4, it is provided that, already before ademand for the activation of the drive machine 2 and the coupling of thedrive machine 2 to the drive output 3, the actuation pressure p_E of thefrictionally engaging shift element E is increased from the openingpressure level to the pressure level of the fast-charging pressure at atime point T81. The fast-charging phase of the frictionally engagingshift element E ends at a time point T82, whereby the actuation pressurep_E has been reduced to the pressure level of the charging compensationpressure and is held constant at said pressure level until the end ofthe charging compensation phase, in the present case until the timepoint T83. Following this, the actuation pressure p_E is increased to anintermediate pressure level by a first pressure ramp which lasts until atime point T84 and, following this in turn, is increased further along asecond pressure ramp whose gradient is shallower than the gradient ofthe first pressure ramp which ends at the time point T84. At a timepoint T85 which simultaneously constitutes the end of the secondpressure ramp, a demand for the activation and coupling-on of the drivemachine 2 is triggered, whereby, proceeding from the time point T85, theengine rotational speed n_mot increases towards of the idle rotationalspeed n_motLL as illustrated.

In order that the positively engaging shift element F to be activatedcan be transferred into its closed operating state, the actuationpressure p_E is increased with a steep gradient to a furtherintermediate pressure level proceeding from the time point T85, wherebythe torque transfer capacity of the frictionally engaging shift elementE increases. The increase of the torque transfer capacity of thefrictionally engaging shift element E has the effect that both theprofile of the product n_ab*i_zielgang_sas and the turbine rotationalspeed n_t increase proceeding from a time point T86. Proceeding from atime point T87, it is in turn the case that the actuation pressure p_Eof the frictionally engaging shift element E is reduced as illustratedwith a steep gradient in order to reduce a rotational speed differencein the region between shift element halves of the shift element F. Sincethe profile of the turbine rotational speed n_t increasingly approachesthe profile of the product n_ab*i_zielgang_sas over the operating timet, the actuation pressure p_E of the frictionally engaging shift elementE is reduced further along a further pressure ramp proceeding from atime point T88, the gradient of the further pressure ramp being smallerthan the gradient of the pressure ramp provided between the time pointsT87 and T88.

At a time point T89, the turbine rotational speed n_t substantiallycorresponds to the profile of the n_ab*i_zielgang_sas and it isidentified that the positively engaging shift element F is in anoperating state expedient for the activation. This has the effect thatthe actuation pressure p_F is increased abruptly as illustrated to theclosing pressure level at the time point T89, while the actuationpressure p_E of the frictionally engaging shift element E is reduced tozero and the frictionally engaging shift element E is transferred intoits fully open operating state.

Owing to the actuation of the frictionally engaging shift element Edescribed between the time points T81 and T89, it is the case that, inthe gearbox 4, for the synchronization of the positively engaging shiftelement F to be activated, as a function of the operating state of thegearbox 4 present at the time T74, either the fifth transmission ratio“5”, the sixth transmission ratio “6” or the seventh transmission ratio“7” is at least partially engaged in order to synchronize the positivelyengaging shift element F, and subsequently a downshift is performed inthe gearbox 4 proceeding from the seventh transmission ratio “7”, thesixth transmission ratio “6” or the fifth transmission ratio “5” towardsthe transmission ratio “1”, “2” or “3” to be engaged in the gearbox 4,while the positively engaging shift element F is activated in additionto the further positively engaging shift element A and the frictionallyengaging shift element D, C or B that is already active at the timepoint T80.

FIG. 14 in turn shows multiple profiles of different operating variablesof the vehicle drivetrain 1 versus the time t, wherein the vehicledrivetrain 1 is, at a time point T100 indicated in more detail in FIG.14, in an operating state in which the two positively engaging shiftelements A and F are closed in the gearbox 4, while the furtherfrictionally engaging shift elements B, C, D and E are present in theopen operating state and the drive machine 2 is in a shut-down state.The profile MSF has the value zero during the entire operating stateprofile of the vehicle drivetrain 1 under consideration, because theengine-stop enable signal is active.

This operating state of the vehicle drivetrain 1 is established owing toan activation of an engine start-stop function, which allows the drivemachine 2 to be decoupled from the drive output 3 when the vehicle is ata standstill by opening the frictionally engaging shift elements B to E,and the two positively engaging shift elements A and F being held in aclosed operating state in order to be able to engage one of thetransmission ratios “1” to “4” for a launch process with highspontaneity, the launch process being realized in a vehicle equippedwith the vehicle drivetrain 1, because it is then the case that, in eachcase by activation of the shift element D, of the shift element C, ofthe shift element B or of the shift element E, one of said transmissionratios can be engaged within short operating times in the gearbox 4.Owing to the fact that the drive output rotational speed n_ab of thedrive output 3 is greater than zero, the profile of the productn_ab*i_zielgang_sas sets as shown in FIG. 14, wherein the variablei_zielgang_sas in turn corresponds to the transmission ratio to beengaged in the gearbox 4 upon a departure from the engine start-stopfunction.

Owing to gearbox-internal drag torques, the rotational speed n_t of thegearbox input shaft 6 is greater than zero. At a time point T101, it isidentified in the region of a superordinate driving strategy that theclutch logic presently selected by the activated engine start-stopfunction causes undesirably high drag torques in the region of thegearbox 4 owing to the determined ratio between the turbine rotationalspeed n_t and the drive output rotational speed n_ab of the drive output3. For this reason, a demand is triggered for realizing a sailingoperating function of the vehicle drivetrain 1 during which, as afunction of the present operating state of the vehicle drivetrain 1, thepositively engaging shift element F has to be transferred into its openoperating state first.

For this purpose, at the time point T101, an actuation pressure p_F ofthe positively engaging shift element F is decreased abruptly from theclosing pressure level to zero. At a time point T102 which followsshortly thereafter, the open operating state of the positively engagingshift element F with simultaneously closed positively engaging shiftelement A is identified, and furthermore, in the presence of an activesailing operating function, an operating state of the vehicle drivetrain1 is identified in which the third transmission ratio “3” for forwardtravel has to be engaged in the gearbox 4 in the event of a deactivationof the sailing operating function. Therefore, an actuation pressure p_Bof the frictionally engaging shift element B is increased to afast-charging pressure level at the time point T102 and is held constantat such pressure level until a time point T103. At the time point T103,the actuation pressure p_B of the frictionally engaging shift element Bis decreased abruptly to the pressure level of the charging compensationpressure and is in turn held constant at said pressure level until theend of the charging compensation phase, in the present case until a timepoint T105.

Subsequently, the actuation pressure p_B is increased by two successivepressure ramps to an intermediate pressure level at which thefrictionally engaging shift element B is present in its slippage-freeoperating state until a time point T106. Upon attainment of saidoperating state of the frictionally engaging shift element B, theactuation pressure p_B of the frictionally engaging shift element B isincreased to the closing pressure level, whereby the frictionallyengaging shift element B is fully closed.

In order to be able, at the time point T101, to transfer the positivelyengaging shift element F as desired into its open operating state, it ispossible, in an embodiment of the gearbox 4 in which the positivelyengaging shift element F is charged with hydraulic pressure in order tobe opened, for a system pressure of the gearbox 4 to be increased andfor a possibly installed electrical auxiliary oil supply to be adjustedto a higher power point if the actuation pressure p_F which is to beapplied to the positively engaging shift element F to be opened andwhich acts in the opening direction is dependent on the system pressureor on the electrical auxiliary oil supply implemented as an electricalauxiliary pump.

During the charging compensation phase of the frictionally engagingshift element B, at a time point T107 which in the present case liesbetween the time points T103 and T105, an actuation pressure p_C of thefrictionally engaging shift element C is increased to the fast-chargingpressure level and is maintained at said pressure level until the end ofthe fast-charging phase at the time point T108. At the time point T108the actuation pressure p_C of the frictionally engaging shift element Cis reduced to the charging compensation pressure level and is maintainedat said pressure level until the time point T106, at which thefrictionally engaging shift element B is transferred into its closedoperating state. Proceeding from the time point T106, the actuationpressure p_C of the frictionally engaging shift element C is likewisetransferred by two successive pressure ramps into its slippage-freeoperating state and is transferred into its fully closed operating stateat the time point T109 by increasing the actuation pressure p_C.

Furthermore, during the charging compensation phase of the frictionallyengaging shift element C, an actuation pressure p_D of the frictionallyengaging shift element D is increased to the fast-charging pressurelevel at a time point T110 which lies between the time points T108 andT106 and the actuation pressure p_D of the frictionally engaging shiftelement D is reduced to the charging compensation pressure level at atime point T111 which lies between the time points T106 and T109. Thecharging compensation phase of the frictionally engaging shift element Dis ended at a time point T112, and at the time point T112, the actuationpressure p_D is increased by two pressure ramps until the time pointT113 to an intermediate pressure level at which the frictionallyengaging shift element D is likewise present in the slippage-freeoperating state. Upon attainment of this operating state, the actuationpressure p_D of the frictionally engaging shift element D is in turnincreased to the closing pressure level, whereby, in addition to theshift elements A, B and C, the frictionally engaging shift element D isalso present in its fully closed operating state. In the closedoperating state of the frictionally engaging shift elements C, D and E,the gear set 5 of the gearbox 4 is in the partially blocked operatingstate, in which the gearbox input shaft 6 is held rotationally fixed andthe gearbox output shaft 9 connected to the drive output 3 is rotatable.For this reason, the turbine rotational speed n_t continuously decreasestowards zero proceeding from the time point T105.

Since, at the time point T113, the frictionally engaging shift element Dis also transferred into its closed operating state, the sailingoperating state of the vehicle drivetrain 1 demanded at the time pointT101 is activated as desired at the time point T113.

By contrast to the above-described charging sequence of the frictionallyengaging shift elements B, C and D, it is provided that, proceeding froman operating state of the vehicle drivetrain 1 at the time point T101 inwhich, upon a departure from the sailing operating function, the secondtransmission ratio “2” for forward travel has to be engaged in thegearbox 4 as target gear in accordance with the demand zielgang_sas inorder to establish the power flow between the drive machine 2 and thedrive output 3 and proceeding from a situation in which the positivelyengaging shift elements A and F are present in the closed operatingstate, the frictionally engaging shift element C is transferred into itsclosed operating state first proceeding from the time point T102 in amanner corresponding to the actuation of the frictionally engaging shiftelement B, and, already during the charging compensation phase of thefrictionally engaging shift element C, the frictionally engaging shiftelement D rather than the frictionally engaging shift element C isprepared for activation in the described manner proceeding from the timepoint T107. Subsequently it is finally the case that the frictionallyengaging shift element B rather than the frictionally engaging shiftelement D is transferred into its closed operating state over the periodfrom the time point T111 to the time point T113.

By contrast to this, in the presence of an operating state of thevehicle drivetrain 1 at the time point T101 in which, upon adeactivation of the sailing operating state, the first transmissionratio “1” for forward travel has to be engaged in the gearbox 4, it isprovided that first the shift element D, then the shift element C and inturn subsequently the shift element B is transferred into its closedoperating state respectively, in order to achieve the advantages,described in each case further below, in the event of a departure fromthe sailing operating state of the vehicle drivetrain 1 during theactivation of the sailing operating function between the time pointsT101 and T113.

For the case in which the further positively engaging shift element F,despite corresponding actuation, is not present in its open operatingstate at the time point T102, or the superordinate driving strategyidentifies high drag torques in the region of the gearbox 4 whichprevent an opening of the positively engaging shift element F asdescribed with regard to FIG. 3, approaches discussed in more detailbelow with regard to FIG. 4 are implemented in order to transfer thepositively engaging shift element F as desired into its open operatingstate.

The profiles of the operating variables described in FIG. 15 of thevehicle drivetrain 1 as per FIG. 1 form the basis, at the time pointT102, of an operating state profile in which, higher drag torquesprevail at the positively engaging shift element F than in the operatingstate of the vehicle drivetrain 1 at the time point T102 as per FIG. 14.For this reason, proceeding from the time point T102 as per FIG. 15, itis provided that, firstly, for the activation of the sailing operatingstate, the actuation pressure p_B of the frictionally engaging shiftelement B is charged with a fast-charging pulse by a correspondingincrease of the actuation pressure p_B in the manner illustrated in FIG.4 until the time point T104 and the frictionally engaging shift elementB is reduced to the level of the charging compensation pressure at thetime point T104. Furthermore, at the time point T104, the frictionallyengaging shift element E is charged with a fast-charging pulse by anincrease of its actuation pressure p_E until a time point T114, andduring a subsequent charging compensation phase which lasts until a timepoint T115, said frictionally engaging shift element E is actuated withan actuation pressure p_E at a charging compensation pressure level andis thus prepared for the activation. At the time point T115, thefrictionally engaging shift element E is in an operating state in whichthe torque transfer capacity of the frictionally engaging shift elementE is substantially equal to zero, and an increase of the actuation forceresults in an immediate increase of the torque transfer capacity of thefrictionally engaging shift element E.

Furthermore, the actuation pressure of the positively engaging shiftelement F to be deactivated is reduced to zero shortly after the timepoint T114. Proceeding from the time point T115, the actuation pressurep_E is increased along a first pressure ramp which ends at the timepoint T116. Subsequently the actuation pressure p_E of the frictionallyengaging shift element E is increased further in continuous fashion by afollowing further pressure ramp, which in the present case ends at thetime point T117 and has a shallower gradient than the pressure rampprovided between the time points T115 and T116. Following this, theactuation pressure p_E is in turn increased to a greater extent along afurther pressure ramp, the gradient of which is in turn steeper than thegradient of the pressure ramp between the time points T116 and T117,until finally, the open operating state of the positively engaging shiftelement is identified at a time point T118. The successive increase ofthe torque transfer capacity of the frictionally engaging shift elementE results in a reduction in load on the shift element F, or a loweringof the torque which acts on the shift element F and which counteractsthe desired opening of the shift element F. At the time point T118, thetorque that prevails at the positively engaging shift element F has beenreduced as a result of the increase of the torque transfer capacity ofthe frictionally engaging shift element E, to such an extent that thepositively engaging shift element F transitions into its open operatingstate.

Upon identification of the open operating state of the shift element F,the actuation pressure p_E of the frictionally engaging shift element Eis, proceeding from the time point T118, reduced as illustrated along apressure ramp with a steep gradient until a time point T119 to anintermediate pressure level which lies below the charging compensationpressure level, whereby the frictionally engaging shift element E ispresent in the open operating state at or before the time point T119. Atthe time point T119, the actuation pressure p_E is reduced to zeroagain, whereby the frictionally engaging shift element E transitionsinto its fully deactivated operating state.

Shortly thereafter the actuation pressure p_B of the frictionallyengaging shift element B is increased at a time point T120, as discussedin more detail with regard to FIG. 14, proceeding from the chargingcompensation pressure level along the two pressure ramps to theintermediate pressure level, at which the frictionally engaging shiftelement B is present in the slippage-free operating state. To fullyactivate the frictionally engaging shift element B, the actuationpressure p_B is increased abruptly to the closing pressure level at thetime point T121, whereby the frictionally engaging shift element B isfully activated. In the activated operating state of the frictionallyengaging shift element B, the frictionally engaging shift element C isfirst charged with a fast-charging pulse proceeding from a time pointT122 and is prepared for the activation during a charging compensationphase which follows said fast-charging pulse and which lasts until atime point T123. At the time point T124, the frictionally engaging shiftelement C is in its slippage-free operating state, as a result of whichthe actuation pressure p_C is increased again, in the manner describedabove, to the closing pressure level at the time point T124.

Before the end of the charging compensation phase of the frictionallyengaging shift element C, the frictionally engaging shift element D islikewise charged with a fast-charging pulse proceeding from a time pointT125, and is prepared for the activation during a charging compensationphase which follows said fast-charging pulse and which lasts until atime point T126. At the time point T127, the frictionally engaging shiftelement D is likewise in its slippage-free operating state, as a resultof which the actuation pressure p_D of the frictionally engaging shiftelement D is increased to the closing pressure level at the time pointT127, whereby the vehicle drivetrain 1 is present in its demandedsailing operating state at the time point T127.

If, at the time point T102, it is identified by the superordinatedriving strategy that the second transmission ratio “2” rather than thethird transmission ratio “3” for forward travel has to be engaged in theevent of a termination of the activation of the sailing operating state,the actuation pressure p_C of the frictionally engaging shift element Crather than the actuation pressure p_B of the frictionally engagingshift element B is set in the manner described with regard to FIG. 4 atthe time point T102. After the end of the fast-charging phase of thefrictionally engaging shift element C the actuation pressure p_E of thefrictionally engaging shift element E is correspondingly set in order torelieve the positively engaging shift element F of load. Furthermore, atthe time point T122, the actuation pressure p_D of the frictionallyengaging shift element D and subsequently at the time point T125 theactuation pressure p_B of the frictionally engaging shift element B areset in the manner described above in order to transfer the shiftelements C and D respectively into their fully closed operating state atthe time points T124 and T127.

If, by contrast to this, at the time point T102, an operating state ofthe vehicle drivetrain 1 is identified proceeding from which the firsttransmission ratio “1” for forward travel has to be engaged in thegearbox 4 in the event of a termination of the activation of the sailingoperating function, first the frictionally engaging shift element Drather than the frictionally engaging shift element B or frictionallyengaging shift element C is actuated proceeding from the time point T102in the manner described above with regard to FIG. 4, before thefrictionally engaging shift element E is introduced into the power flowof the gearbox 4 in order to relieve the positively engaging shiftelement F of load. Subsequently, it is in turn the case that first thefrictionally engaging shift element C is adjusted in the direction ofits fully closed operating state and during the activation process ofthe frictionally engaging shift element C the frictionally engagingshift element B is likewise adjusted in the direction of its fullyclosed operating state proceeding from the time point T125, in order toultimately activate the sailing operating state of the vehicledrivetrain 1 as desired at the time point T127.

Furthermore, the approaches described in more detail below may be calledupon by the superordinate driving strategy in order to operate oractuate the vehicle drivetrain 1 and in particular the gearbox 4 suchthat, in the presence of a demand for activation of the sailingoperating state of the vehicle drivetrain 1 during its activationprocess, a departure from sailing triggered by present changes inoperating state of the vehicle drivetrain 1 can be implemented with highspontaneity with simultaneously high levels of driving comfort.

If a corresponding demand for deactivation of the sailing operatingfunction is present during an operating state profile of the vehicledrivetrain 1 as per FIG. 3 before the time point T101, the twopositively engaging shift elements F and A are left in the activatedoperating state and, in a manner dependent on the transmission ratio tobe engaged in each case in the region of the gearbox 4, the frictionallyengaging shift element to be activated for this purpose is activatedwithin short operating times and with desired high spontaneity withsimultaneously high levels of driving comfort.

By contrast to this, the shift elements B, C or D, which are alreadyactuated before the time point T114 as described with regard to FIG. 15,and the frictionally engaging shift element E are discharged again andthe positively engaging shift elements F and A are left in the activatedoperating state if a demand for deactivation of the sailing operatingfunction is triggered before the time point T114 and, subsequently, thefrictionally engaging shift element to be activated in each case inorder to realize the demanded operating state of the vehicle drivetrain1 is engaged or the frictionally engaging shift elements are, in thepresence of an active engine start-stop function, held in an openoperating state.

If the demand for deactivation of the sailing operating function istriggered at a time point at which the positively engaging shift elementF is already being actuated in an opening direction and, owing to theactuation, has transitioned into its open operating state, one of thetransmission ratios “5”, “6” or “7” for forward travel, for therealization of which the further positively engaging shift element F hasto be held in or transferred into the open operating state, is engagedin the gearbox 4 first.

If, during the activation of the sailing operating state of the vehicledrivetrain 1, the gearbox 4 is actuated, owing to a present operatingstate of the vehicle drivetrain 1 such that, upon a departure fromsailing, the third transmission ratio “3” for forward travel can beengaged in the gearbox 4 with high spontaneity merely by activating thepositively engaging shift element F, it is provided that, in thepresence of a demand for the deactivation of the sailing operatingfunction, the fifth transmission ratio “5” is engaged in the gearbox 4first and subsequently the positively engaging shift element F istransferred into its closed operating state during a downshift towardsthe third transmission ratio “3” in accordance with a conventional shiftsequence. At the same time, the frictionally engaging shift element E isdeactivated during the downshift from the fifth transmission ratio “5”towards the third transmission ratio “3”. Depending on the respectivelydemanded operating state, the frictionally engaging shift element B isheld in the closed operating state or is transferred into its openoperating state. The latter is the case if, for example, the enginestart-stop function is activated and a decoupled operating state of theshut-down drive machine 2 is demanded.

When the vehicle is at a standstill, the frictionally engaging shiftelement B is thus transferred into its closed operating state and thetwo further frictionally engaging shift elements C and D are transferredinto their open operating state if they are already charged or closed.If the shift elements C and D are not yet charged or not yet closed, thecharging process of the frictionally engaging shift elements C and D isno longer started. In addition to the frictionally engaging shiftelement B, the frictionally engaging shift element E has to betransferred into its closed operating state in order to engage the fifthtransmission ratio “5” in the gearbox 4 as required, to subsequentlysynchronize the positively engaging shift element to be activated, andto transfer the latter into the closed operating state during thedownshift proceeding from the fifth transmission ratio “5” towards thethird transmission ratio “3”.

By contrast to this, if the demand for deactivation of the sailingoperating function triggers an operating state of the vehicle drivetrain1 proceeding from which the second transmission ratio “2” for forwardtravel has to be engaged in the gearbox 4, the frictionally engagingshift element C is closed or held in its closed operating state whilethe frictionally engaging shift elements D and B are held in ortransferred into their open operating states. By contrast to thedeparture from sailing into the third transmission ratio “3” for forwardtravel, as described above, in the event of a departure from sailing inthe direction of the second transmission ratio “2” for forward travel,instead of the synchronization gearspeed “5” which calls for thepositively engaging shift element F to be activated, the sixthtransmission ratio “6” is engaged first as synchronization gearspeed inthe gearbox 4, and subsequently, the positively engaging shift element Fis synchronized and in the process transferred into its closed operatingstate during a downshift proceeding from the sixth transmission ratio“6” towards the second transmission ratio “2”.

By contrast, if the first transmission ratio “1” for forward travel hasto be engaged in the gearbox 4 upon a departure from sailing, thefrictionally engaging shift element D has to be closed or held in itsclosed operating state, while the two other frictionally engaging shiftelements C and B have to be opened or held in their open operatingstates. Following this, the further frictionally engaging shift elementE is transferred into its closed operating state in order to firstengage the seventh transmission ratio “7” in the gearbox “4”, whichconstitutes the so-called synchronization gear for the positivelyengaging shift element F to be activated. Proceeding from the seventhtransmission ratio “7” for forward travel which is then engaged in theregion of the gearbox 4, a downshift is performed in the direction ofthe first transmission ratio “1” for forward travel by opening thefrictionally engaging shift element E and by closing the positivelyengaging shift element F, whereby the operating state of the vehicledrivetrain 1 to be established as a result of the demanded departurefrom sailing is present.

Furthermore, using the superordinate driving strategy, in the presenceof a demand for a departure from sailing as a result of a demand forload during the above-described charging sequence of the frictionallyengaging shift elements B, E, C and D, a further approach may beselected. Using the selected approach, as a function of a possibly newtarget gear setpoint and the time point at which the target gear changetakes place during the charging sequence of the frictionally engagingshift elements B, E, C and D, a termination of the charging sequence orthe next clutch B, E, C and D to be closed is selected such that agreater downshift gearspeed step is possible proceeding from theprepared operating state of the gearbox 4.

Thus, in the presence of a demand for departure from sailing and atarget gear change proceeding from the third transmission ratio “3” inthe direction of the second transmission ratio “2”, the frictionallyengaging shift element C is transferred into its closed operating stateand the frictionally engaging shift elements B and D are opened, or thecharging thereof is omitted. Subsequently, in turn, the frictionallyengaging shift element E is closed for the engagement of thesynchronization gear or, more specifically, for the sixth transmissionratio “6”, and the positively engaging shift element F to be engaged isengaged during the downshift towards the second transmission ratio “2”.

If, owing to a demand for load, a transition into sailing with a targetgear change from the third transmission ratio “3” towards the firsttransmission ratio “1” for forward travel is present, the frictionallyengaging shift element D is transferred into or left in its closedoperating state, while the frictionally engaging shift elements B and Care transferred into or left in their fully open operating state.Furthermore, the frictionally engaging shift element E is closed inorder to engage in the gearbox 4 the synchronization gear for thepositively engaging shift element F to be closed or, more specifically,for the seventh transmission ratio “7”, and subsequently transfer thepositively engaging shift element F into its synchronized operatingstate and close said positively engaging shift element F during thedownshift towards the first transmission ratio “1”.

FIG. 16 shows multiple profiles of different operating variables of thevehicle drivetrain 1 versus the time t, wherein the vehicle drivetrain 1is, at a time point T40 denoted in more detail in FIG. 16, in anoperating state in which the second transmission ratio “2” is engaged inthe gearbox 4 and the rotational speed n_mot of the drive machine 2 ishigher than the idle rotational speed n_motLL of the drive machine 2. Atthe time point T40, it is checked whether the drive machine 2 has to betransferred into a shut-down operating state by an engine start-stopfunction or by a sailing operating function. Based on the precedingoperating state profile of the vehicle drivetrain 1, a demand forrealizing the sailing operating state of the vehicle drivetrain 1 istriggered at the time point T40, during which the drive machine 2 is ina shut-down state and the power flow between the drive machine 2 and thedrive output 3 is disconnected in the region of the gearbox 4.

Here, the demand for the activation of the sailing operating state istriggered proceeding from an operating state of the vehicle drivetrain 1in which the drive machine 2 is active and is connected to the driveoutput 3 by the gearbox 4. Furthermore, the rotational speed n_ab of thedrive output 3 is greater than zero, wherein the vehicle equipped withthe vehicle drivetrain 1 is in an operating state close to standstill.As already discussed above, in addition to the two positively engagingshift elements A and F, the frictionally engaging shift element C isactive and the second transmission ratio “2” for forward travel isengaged in the gearbox 4, while the shift elements B, D and E are eachpresent in the open operating state. For this purpose, the shiftelements A to F are charged with the actuation pressures p_A to p_Frespectively required for this purpose.

Proceeding from a time point T41, for activation of the sailingoperating state, it is provided that the frictionally engaging shiftelement E is charged with a fast-charging pulse by a correspondingincrease of an actuation pressure p_E in the manner illustrated in FIG.16 until a time point T42, and said frictionally engaging shift elementE is actuated with an actuation pressure p_E at a charging compensationpressure level during a subsequent charging compensation phase whichlasts until a time point T43, and is thus prepared for the activation.At the time point T43, the frictionally engaging shift element E is inan operating state in which the torque transfer capacity of thefrictionally engaging shift element E is substantially equal to zero,and an increase of the actuation force results in an immediate increaseof the torque transfer capacity of the frictionally engaging shiftelement E.

Furthermore, proceeding from the time point T40, the rotational speedn_mot of the drive machine 2 is adjusted increasingly towards the idlerotational speed n_motLL in the illustrated manner. The increase of thetorque transfer capacity of the frictionally engaging shift element Eproceeding from the time point T43 along a pressure ramp which lastsuntil a time point T44 has the effect that the positively engaging shiftelement F transitions into an at least approximately load-free operatingstate, and, at a time point T45 which lies between the time points T43and T44, the actuation pressure p_F of the further positively engagingshift elemenet F is decreased in abrupt fashion by correspondinglysetting the actuation pressure p_F of the positively engaging shiftelement F from a pressure value which corresponds to the closedoperating state of the positively engaging shift element F to a pressurevalue which corresponds to the open operating state of the positivelyengaging shift element F. The activation of the frictionally engagingshift element E has the effect that the positively engaging shiftelement F is transferred into an at least load-free operating state.Said operating state is attained by the positively engaging shiftelement F at the deactivation time point T45.

Proceeding from the time point T44 the actuation pressure p_E of thefrictionally engaging shift element E is increased along a furtherpressure ramp until a time point T46, the gradient of the furtherpressure ramp being shallower than that of the pressure ramp providedbetween the time points T43 and T44. Proceeding from the pressure levelof the actuation pressure p_E prevailing at the time point T46, theactuation pressure p_E is increased along a third pressure ramp to ahigher pressure level until a time point T47, the gradient of the thirdpressure ramp being in turn steeper than the gradient of the twopreceding pressure ramps. At the time point T47, it is identified that arotational speed n_t of the gearbox input shaft 6, deviates from aproduct of the rotational speed n_ab of the drive output 3 and thetransmission ratio i_zielgang_sas presently engaged in the gearbox 4 atthe time point T40. If the deviation between the turbine rotationalspeed n_t and the product of the rotational speed n_ab of the driveoutput 3 and the transmission ratio i_zielgang_sas exceeds the thresholdvalue kfl, then in the present case, the disconnected power flow betweenthe drive machine 2 and the drive output 3 in the region of the gearbox4 is identified. This is the case here at the time point T47.

At the time point T47, the sixth transmission ratio “6” is at leastpartially engaged in the gearbox 4 owing to the shift elements C and Abeing present in the closed operating state and the at least partiallyactivated frictionally engaging shift element E. It is provided that, ata time point T48 which follows the time point T47, the frictionallyengaging shift element B is prepared for the activation or, morespecifically, closure, in the manner illustrated in FIG. 16, by afast-charging phase, which lasts until a time point T47, and asubsequent charging compensation phase, which ends at a time point T50.This is because, in the presence of an active sailing operating state atthe present operating point of the vehicle drivetrain 1, withprogressive operating time t, the third transmission ratio “3” forforward travel has to be engaged in the gearbox rather than the sixthtransmission ratio “6” for forward travel in the event of a departurefrom the sailing operating state in the gearbox 4. An additional reasonis that, in order to realize operation of the vehicle drivetrain 1 withthe greatest possible efficiency, the power flow between the drivemachine 2, which is to be shut down, and the drive output 3 has to bedisconnected in the gearbox 4.

At a time point T51 which follows the time point T49, the demand for theshutdown of the drive machine 2 is triggered, as a result of which therotational speed n_mot of the drive machine 2 decreases towards zero.The demand corresponding to this results from the profile MSF, which atthe time point T51 jumps from the value 0 to the value 1 and thusactivates the engine-stop enable signal. Thus, at the time point T45,the sailing operating state demanded at the time point T40 is activatedas desired.

Shortly after the time point T47 at which the open operating state ofthe positively engaging shift element F is identified, the actuationpressure p_E of the frictionally engaging shift element E is, proceedingfrom a time point T52 which lies between the time point T48 and T49,reduced first, in the manner illustrated in FIG. 16, by a pressure rampwhich lasts until the time point T51, and the actuation pressure p_E ofsaid frictionally engaging shift element E is subsequently reduced inabrupt fashion to zero at the time point T51, whereby the frictionallyengaging shift element E transitions into its fully open operating stateand the power flow between the drive machine 2 and the drive output 3 isdisconnected in the region of the gearbox 4.

At the time point T50, the frictionally engaging shift element B ispresent in an operating state in which the torque transfer capacity ofthe frictionally engaging shift element B is substantially equal to zeroand an increase of the actuation force of the frictionally engagingshift element B or of the actuation pressure p_B results in an immediateincrease of the torque transfer capacity of the frictionally engagingshift element B. Proceeding from the time point T50, the actuationpressure p_B of the frictionally engaging shift element B is increasedas illustrated by two successive pressure ramps until a time point T53,at which the frictionally engaging shift element B is present in theslippage-free operating state. For this reason, at the time point T53,the actuation pressure p_B of the frictionally engaging shift element Bis increased in abrupt fashion to the closing pressure level, at whichthe frictionally engaging shift element B is fully closed. Thus, at thetime point T53, the three shift elements A, B and C are closed, as aresult of which the gear set 5 of the gearbox 4 is present in apartially blocked operating state, in which the gearbox input shaft 6 isheld rotationally fixed and the gearbox output shaft 9 connected to thedrive output 3 is rotatable.

In the case of the operating state profile of the vehicle drivetrain 1described in more detail above, the sailing operating state or thesailing operating function is for example activated proceeding from anoperating state of a vehicle close to a standstill if it issimultaneously identified that a profile of the rotational speed n_ab ofthe drive output 3 has a positive gradient and, nevertheless, the drivemachine 2 has to be transferred into its shut-down operating state. Thisis the case for example if a power demand from a driver remains absentduring simultaneous downhill travel of a vehicle, or a vehicle isimplemented with an electrically driveable vehicle axle and it isidentified that the present power demand from the driver can beimplemented using said electrically driveable vehicle axle alone.

In the event of a demand for activation of the sailing operating statebeing detected, the frictionally engaging clutch or, more specifically,the frictionally engaging shift element E which relieves the positivelyengaging shift element F, which is to be deactivated, of load isactuated. During the charging process of the frictionally engaging shiftelement E and the associated build-up phase of the relief torque in theregion of the positively engaging shift element F, the actuation of thepositively engaging shift element F, which is to be disengaged, in theopening direction is triggered.

If the positively engaging shift element F is rendered virtually freefrom torque by the relief torque built up in the region of thefrictionally engaging shift element E, the positively engaging shiftelement F is opened without generating a relief shock in the vehicledrivetrain 1. If the open operating state of the positively engagingshift element F is detected, for example through a corresponding travelsensor arrangement in the region of the positively engaging shiftelement F or a correspondingly identified rotational speed reaction inthe region of the gearbox 4, the relief torque built up in the region ofthe frictionally engaging shift element E is reduced by reduction of theactuation pressure p_E and the resulting pressure dissipation in theregion of the relief clutch or, more specifically, in the region of thefrictionally engaging shift element E, and thus the drive output 3 isdecoupled from the drive machine 2, and thus the power transmission tothe gearbox output is eliminated.

In this operating state of the vehicle drivetrain 1 that is thenpresent, the vehicle equipped with said drivetrain 1 thus coasts withthe drive machine 2 initially still active. To be able to operate thevehicle drivetrain 1 with the drive machine 2 shut down, frictionallyengaging shift elements of the gearbox 4 are charged and transferredinto their closed operating state in each case in a manner dependent onthe present operating state of the vehicle drivetrain 1. Since thegearbox output shaft 9 and the drive output 3 connected rotationallyconjointly thereto can already rotate freely, the charging of thosefrictionally engaging shift elements of the gearbox 4 which have to beactivated and transferred into the closed operating state can beperformed within short operating times.

Proceeding from this operating state of the vehicle drivetrain 1, it ispossible, in the presence of an active sailing operating function, forthe gearbox 4 to in each case be correspondingly actuated in a mannerdependent on the respectively present operating state profile of thevehicle drivetrain 1 in order to achieve an operating state to beestablished in the region of the gearbox 4 in the event of a departurefrom the coasting operating state with high spontaneity. For thispurpose, the shift elements A to F are actuated in each case in a mannerdependent on the present operating point of the vehicle drivetrain 1 andin the presence of a simultaneously active sailing operating function,wherein the actuation of the shift elements A to F is performed to amajor extent in a manner dependent on the rotational speed n_ab of thedrive output 3 of the vehicle drivetrain 1 in order to be able torealize gearspeed tracking that is required for high spontaneity.

FIG. 17 shows the profiles of the operating variables of the vehicledrivetrain 1 illustrated in FIG. 16, proceeding from an operating stateat a time point T54 at which the power flow between the drive machine 2and the drive output 3 is enabled in the region of the gearbox 4 and thefourth transmission ratio “4” for forward travel is engaged in thegearbox 4. As can be seen from the shift table as per FIG. 2, to realizethe fourth transmission ratio “4” for forward travel, not only the twopositively engaging shift elements A and F but also the frictionallyengaging shift element E have to be closed in the gearbox 4. Therotational speed n_mot of the drive machine 2 and the value of theproduct n_ab*i_zielgang_sas lie above the idle rotational speed n_motLL.Up to a time point T55, the profile of the product n_ab*i_zielgang_sasis equal to the profile of the turbine rotational speed n_t.

Owing to the operating state profile present at the time point T54, ademand for activation of the sailing operating function of the vehicledrivetrain 1 is triggered by the superordinate driving strategy. Torealize the sailing operation, the positively engaging shift element Fhas to be deactivated. Since a torque prevails at the positivelyengaging shift element F which counteracts the opening process of thepositively engaging shift element F, the actuation pressure p_B of thefrictionally engaging shift element B is increased abruptly from zero tothe fast-charging pressure level at the time point T55 and is heldconstant at said pressure level until a time point T56.

At the time point T56, the actuation pressure p_B is reduced to thecharging compensation pressure level and, in turn, is held at saidpressure level until a time point T57. Proceeding from the time pointT57, the actuation pressure p_B is increased from the chargingcompensation pressure level with a defined gradient along a firstpressure ramp which, in the present case, ends at a time point T58. Atthe time point T57, the frictionally engaging shift element B to beactivated is in an operating state in which the torque transfer capacityof the frictionally engaging shift element B is equal to zero and anincrease of the actuation pressure p_B which acts in the closingdirection of the frictionally engaging shift element B results in animmediate increase of the torque transfer capacity of the frictionallyengaging shift element B. Owing to the latter change in operating stateof the frictionally engaging shift element B, the positively engagingshift element F to be deactivated is progressively relieved of loadproceeding from the time point T57. At a time point T59 which liesbetween the time points T57 and T58, the positively engaging shiftelement F to be deactivated is in an operating state relieved of load,such that, as a result of an abrupt reduction, from the closing pressurelevel to zero, of the actuation pressure p_F which acts in the closingdirection on the positively engaging shift element F to be deactivated,the positively engaging shift element F transitions into its openoperating state at the time point T59 in accordance with the demand.

Proceeding from the time point T58, the pressure ramp of the actuationpressure p_B of the frictionally engaging shift element B to beactivated is followed by a further pressure ramp, the gradient of saidfurther pressure ramp is shallower than the gradient of the firstpressure ramp which ends at the time point T58. The second pressure rampends at a time point T60, at which the frictionally engaging shiftelement B to be activated is present substantially in the closedoperating state. For this reason, at the time point T60 the actuationpressure p_B is increased abruptly to the closing pressure level, andthe frictionally engaging shift element B is transferred into its fullyclosed operating state. At the time point T60, the actuation pressurep_E of the frictionally engaging shift element E is reduced abruptlyfrom the closing pressure level to an intermediate pressure level abovethe pressure threshold pf_min+HYS. Subsequently, the actuation pressurep_E is adjusted along a pressure ramp, which in the present case ends ata time point T61, to an intermediate pressure level below the pressurethreshold pf_min+HYS, and at the time T61, said actuation pressure isreduced abruptly to zero, whereby the frictionally engaging shiftelement E transitions into its fully open operating state.

Using the approach implemented between the time points T54 and T61, thepositively engaging shift element F which is activated over a period upto the time point T59 is firstly transferred into an at leastapproximately load-free operating state by an at least partialengagement of the fifth transmission ratio “5” in the gearbox 4, for therealization of which the positively engaging shift element F has to betransferred into the open operating state and the torque transfercapacity of the frictionally engaging shift element B has to be varied.When the at least approximately load-free operating state is achieved atthe time point T59, the positively engaging shift element F is opened asdescribed above, whereby the demand for realizing the sailing operatingstate can be implemented with high spontaneity.

In a manner dependent on the present operating state profile of thevehicle drivetrain 1, it is identified in the region of thesuperordinate driving strategy, at a time point T62, which in thepresent case lies between the time points T60 and T61, that the thirdtransmission ratio “3” for forward travel has to be engaged in thegearbox 4 in the event of a departure from sailing. For this reason, atthe time point T62, the actuation pressure p_C of the frictionallyengaging shift element C is increased abruptly to the pressure level ofthe fast-charging pressure and is held constant at said pressure leveluntil the end of the fast-charging phase. Subsequently, the actuationpressure p_C of the frictionally engaging shift element C is, in amanner not illustrated in any more detail, first increased to thepressure level of the charging compensation pressure and subsequently tothe intermediate pressure level during two successive pressure rampswith different gradients, at which the frictionally engaging shiftelement C is present in the slippage-free operating state. When saidoperating state of the frictionally engaging shift element C isattained, the actuation pressure p_C is increased to the closingpressure level and the frictionally engaging shift element C is fullyclosed.

Modifications and variations can be made to the embodiments illustratedor described herein without departing from the scope and spirit of theinvention as set forth in the appended claims.

REFERENCE DESIGNATIONS

-   1 Vehicle drivetrain-   2 Drive machine-   3 Drive output-   4 Gearbox-   5 Gear set-   6 Gearbox input shaft-   7 Hydrodynamic torque converter-   8 Converter lock-up clutch-   9 Gearbox output shaft-   10 Component fixed with respect to a housing-   “1” to “9” Transmission ratio for forward travel-   “R” Transmission ratio for reverse travel-   A to F Shift element-   HR1 to HR4 Internal gear-   zielgang_sas Transmission ratio presently to be engaged in the    gearbox-   i_zielgang_sas Transmission ratio-   kfl Threshold value-   MSF Profile-   n_ab Rotational speed of the drive output-   n_mot, n_mot1 Rotational speed of the drive machine-   n_motEGS Profile of the EGS engine target rotational speed setpoint-   n_motLL Idle rotational speed-   n_t Turbine rotational speed-   p_A Actuation pressure of the shift element A-   p_B Actuation pressure of the shift element B-   p_C Actuation pressure of the shift element C-   p_D Actuation pressure of the shift element D-   p_E Actuation pressure of the shift element E-   p_F Actuation pressure of the shift element F-   P1 to P4 Planetary gear set-   pf_min+Hys Pressure threshold-   PR1 to PR4 Planet gear-   S1 to S4 Sun gear-   ST1 to ST4 Planetary carrier-   t Time-   T0 to T199 Discrete time point

The invention claimed is:
 1. A method for operating a vehicle drivetrain(1), the vehicle drivetrain (1) having a drive machine (2), a driveoutput (3) and a gearbox (4), the gearbox (4) arranged in power flowbetween the drive machine (2) and the drive output (3), the gearbox (4)having at least one positively engaging shift element (A, F) and aplurality of frictionally engaging shift elements (B, C, D, E), the atleast one positively engaging shift element (A, F) and the plurality offrictionally engaging shift elements (B, C, D, E) selectively closablein order to engage different transmission ratios (“1” to “R”) of thegearbox (4), only some of the transmission ratios (“1” to “R”)engageable with the at least one positively engaging shift element (A,F), the vehicle drivetrain (1) configured such that, during a demand foractivation of an engine start-stop function of the vehicle drivetrain(1), the drive machine (2) is decoupled from the drive output (3), thedrive machine (2) is shut down, and the at least one positively engagingshift element (A, F) is transferred into or kept in a closed operatingstate of the at least one positively engaging shift element (A, F), themethod comprising: when there is the demand for activation of the enginestart-stop function of the vehicle drivetrain (1) and a simultaneouslyshut-down drive machine (2), operating the vehicle drivetrain (1) with asailing operating function of the vehicle drivetrain (1) active, withthe drive machine (2) decoupled from the drive output (3), with thepositively engaging shift element (F) open, and with a rotational speed(n_ab) of the drive output (3) greater than a defined rotational speedat which a rotational speed difference between shift element halves ofthe positively engaging shift element (F) lies within a rotational speedrange within which the positively engaging shift element (F) istransferrable into the closed operating state; and actuating thepositively engaging shift element (F) in a closing direction no laterthan when the defined rotational speed is reached.
 2. The method ofclaim 1, further comprising ending actuation of the positively engagingshift element (F) in the closing direction when, in a standstill stateof the vehicle, an open operating state of the positively engaging shiftelement (F) is identified.
 3. The method of claim 1, further comprising:identifying, when the sailing operating function is active, a presentoperating state of the vehicle drivetrain (1) and the transmission ratio(“1” to “9”) that has to be engaged in the gearbox (4) during a restartof the drive machine (2) as a result of activation of the enginestart-stop function; and holding at least those shift elements (B, C, D)of the plurality of frictionally engaging shift elements (B, C, D, E)which have to be closed in order to engage the transmission ratio (“1”to “9”) that has to be engaged in the gearbox (4) for a departure fromthe sailing operating function in an operating state prepared for anactivation of the shift elements (B, C, D) of the plurality offrictionally engaging shift elements (B, C, D, E).
 4. The method ofclaim 1, further comprising transferring, when the sailing operatingfunction is active, a gear set (5) of the gearbox (4) into an at leastpartially blocked operating state by actuation of multiple frictionallyengaging shift elements (B, C, D) of the plurality of frictionallyengaging shift elements (B, C, D, E), a gearbox input shaft (6) heldrotationally fixed and a gearbox output shaft (9) connected to the driveoutput (3) being rotatable in the at least partially blocked operatingstate.
 5. The method of claim 4, further comprising selecting, dependingon the present operating state profile of the vehicle drivetrain (1), asequence of the shift elements (B, C, D) of the plurality offrictionally engaging shift elements (B, C, D, E) that have to beactuated in succession for the partial blocking of the gear set (5). 6.The method of claim 4, further comprising lowering, when the sailingoperating state of the vehicle drivetrain (1) is active, actuationforces of the frictionally engaging shift elements (B, C, D) of theplurality of frictionally engaging shift elements (B, C, D, E) to alevel at which the frictionally engaging shift elements (B, C, D) of theplurality of frictionally engaging shift elements (B, C, D, E) are stillin a slippage-free operating state and proceeding from which the shiftelements (B, C, D) of the plurality of frictionally engaging shiftelements (B, C, D, E) are activatable or deactivatable within shortoperating times.
 7. The method of claim 6, further comprising:activating the engine start-stop function to depart from the sailingoperating function of the vehicle drivetrain (1); raising the actuationforces of the shift elements (B, C, D, E) of the plurality offrictionally engaging shift elements (B, C, D, E) that have to be heldin or transferred into the closed operating state in order to departfrom the sailing operating function of the vehicle drivetrain (1); andopening the shift elements (B, C, D, E) of the plurality of frictionallyengaging shift elements (B, C, D, E) that are not required to departfrom the sailing operating function of the vehicle drivetrain (1). 8.The method of claim 7, further comprising varying a torque transfercapacity of at least one of the shift elements (B, C, D) of theplurality of frictionally engaging shift elements (B, C, D, E) that isactuated for the at least partial blocking of the gear set (5) so that arotational speed difference required for the closure of a furtherpositively engaging shift element (A) is generated between shift elementhalves of the further positively engaging shift element (A) in the openoperating state of the further positively engaging shift element (A). 9.The method of claim 1, further comprising, during the demand foractivation of the engine start-stop function and an associated demandfor engaging a transmission ratio (“1” to “3”) engageable in the gearbox(4) by closing of the positively engaging shift element (F) and inresponse to identification of the open operating state of the positivelyengaging shift element (F) in a vehicle standstill state: engaging asynchronization transmission ratio (“5” to “7”) in the gearbox (4), thepositively engaging shift element (F) being in the open operating statein the synchronization transmission ratio (“5” to “7”); and thendeactivating a frictionally engaging shift element (B, C or E) of theplurality of frictionally engaging shift elements (B, C, D, E) andclosing the positively engaging shift element (F) in order to implementa subsequent change in transmission ratio proceeding from thesynchronization transmission ratio (“5” to “7”) in the direction of thedemanded transmission ratio (“1” to “3”).
 10. The method of claim 1,further comprising triggering, when the engine start-stop function isactive, a demand for activation of the sailing operating function inresponse to an exceedance of a defined threshold value of the rotationalspeed (n_ab) of the drive output (3).
 11. The method of claim 1, furthercomprising triggering, when the engine start-stop function is active, ademand for activation of the sailing operating function in response toan exceedance of a defined threshold value of the rotational speed(n_ab) of the drive output (3) for longer than a predefined time periodor after a driving distance longer than a defined driving distance hasbeen traveled.
 12. The method of claim 1, further comprising:transferring the positively engaging shift element (F) into an at leastapproximately load-free operating state by at least partial engagementof a transmission ratio (“5”) in the gearbox (4) for the engagement ofwhich the positively engaging shift element (F) has to be transferredinto the open operating state and at least a torque transfer capacity ofone of the frictionally engaging shift elements (B, E) of the pluralityof frictionally engaging shift elements (B, C, D, E) has to be varied;and opening the positively engaging shift element (F) when the at leastapproximately load-free operating state is attained.
 13. The method ofclaim 12, further comprising raising, when the sailing operatingfunction is active, the torque transfer capacity of that frictionallyengaging shift element (B, E) which has to be actuated in order toengage the transmission ratio (“5”) which relieves the positivelyengaging shift element (F) of load from a value of zero to a level whichrelieves the positively engaging shift element (F) of load.
 14. Themethod of claim 1, further comprising transferring, when the openoperating state of the positively engaging shift element (F) isdetected, the frictionally engaging shift element (E) of the pluralityof frictionally engaging shift elements (B, C, D, E) into the openoperating state in order to interrupt the power flow between the drivemachine (2) and the drive output (3) in the gearbox (4).